Mobile migration communications control device

ABSTRACT

Disclosed is a migration communication control device constructed to control a continuous communication between a mobile node and a node unaffected the mobile node&#39;s migration. The migration communication control device comprises a first migration control unit, a second migration control unit on the mobile node, and a third migration control unit on the partner node. The first migration control unit comprises a packet transfer unit and an address post unit. The packet transfer unit receives a packet which was destined for an outdated address of the mobile node, generates a conversion packet which holds an updated address instead of the outdated address, and then transmits the conversion packet, while an address post unit transmits an address post message which indicates the updated address to the third migration control unit. The second migration control unit comprises a migration post unit and a packet resumption unit. The migration post unit transmits to the first migration control unit a migration post message which indicates the updated address when the mobile node migrates to another network while a packet resumption unit receives the conversion packet from both the first migration control unit and the third migration control unit and resumes an original packet from the conversion packet. The third migration control unit comprises a packet conversion unit which converts a destination address of a packet into the updated address, then transmits it to the mobile node.

This is a division of U.S. Ser. No. 08/635,027, filed on Apr. 19, 1996,U.S. Pat. No. 5,845,079 which is a division of U.S. Ser. No. 08/014,766,filed on Feb. 8, 1993, and issued as U.S. Pat. No. 5,517,618 on May 14,1996.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a migration communication controldevice that controls a communication between a mobile node and acorresponding node to enable them to communicate continuously when theformer migrates by managing addresses assigned to the former each timeit migrates across networks.

(2) Description of the Related Art

Recent progress in the field of electronic technology makes it possibleto assemble smaller and lighter portable computers. These portablecomputers referred to as mobile nodes are designed so that they canmigrate across networks: they are unplugged from a network and pluggedin another and communicate with a stationary node. Thus, each of them isassigned a specific address to prove its identity. The address, ingeneral, includes location information as to which network the mobilenodes are currently plugged in, and for this reason, a new address isassigned each time they migrate.

For example, the address composed of a network address unit forspecifying a network in which the mobile node is currently plugged inand a node address unit for proving the mobile node's identity in thenetwork, or the address used in a conventional network architecture suchas Internet Protocol (details of which are in Internet Protocol, RFC791,Jon Postel, September, 1981), they must be changed every time the mobilenodes migrate.

However, once the mobile node migrates to another network, acommunication with the stationary node will be terminated. This isbecause a packet is transmitted to its old address only to be wasted.

Thus, to enable the mobile node and stationary node to communicatecontinuously when the former migrates, it is necessary to control thecommunication by managing the steadily changing address.

To date, two address managing methods have been proposed: one by SonyComputer Science Laboratory Inc. and one by the Department of ComputerScience at Columbia University.

Sony Computer Science Laboratory Inc. proposed a method using VIP(Virtual Internet Protocol), details of which are on “VIP: Lower LayerInternet Protocol”, Fumio Teraoka, Yasuhiko Yokote, Mario Tokoro,Proceed of Data Processing Convention Multimedia Communication andDistributed Processing.

In this method, each mobile node is assigned a VIP (Virtual InternetProtocol) address and a PIP (Physical Internet Protocol) address. Theformer is an unchanged address used in a communication application forpacket transmission and reception; and the latter is an address changedfor every migration to specify an update physical location of the mobilnode. Data related to both addresses are held in a cache of a gateway.Under these conditions, the stationary node transmits a packet to themobile node to the VIP address thereof, and the packet is converted intoanother packet addressed to the PIP address when it passes the gateway,thence transmitted to the mobile node via the gateways placed in a routeonwards. These gateways collect data related to a correlation betweenthe VIP and PIP addresses from the header of the packet upon the receiptthereof, thus updates data in the cache, and hence are able to convertother packets addressed to the VIP addresses into the packets addressedto the PIP addresses based on the correlation entered in the cache.

In this method, in short, the use of the address constituting with theVIP and PIP addresses enables the mobile node and the stationary node tocommunicate continuously when the former migrates.

The Department of Computer Science at Columbia University proposed amethod using an Internet Protocol address of which network address unitdoes not specify the network which the mobile node is currently pluggedin but declares itself to be the mobile node, hence a certain value isgiven as the network address unit to all the mobile nodes. As well, themethod uses an MSS (Mobile Support Station) installed at each network tomanage the IP addresses and control a packet route to the mobile node.The MSS is designed so that it collects data related to the updatephysical location of the mobile nodes by referring other MSSs.

Given these conditions, when the stationary node transmits a packet tothe mobile node when it migrates, it first transmits the packet to afirst MSS installed in its network; thence the first MSS transfers thepacket to a second MSS installed in a network which the mobile node iscurrently plugged in; and finally the second MSS transfers the packet tothe mobile node.

In this method, in short, the use of the MSS enables the mobile node andthe stationary node to continue the communication when the formermigrates.

In the first method, however, all the nodes must be constructed so thatthey understand both the VIP and PIP addresses, causing them to extend ascale functionally, otherwise making it impossible to apply this methodto apparatuses employed in existing networks. In addition, thecommunication via the gateways reduces communication efficiency comparedwith direct packet transmission, because the gateways check whether theyhave received the packet addressed to the VIP address or PIP addresseach time they receive it, as well as whether or not to collect the datatherefrom to update those in the cache.

In the second method, each network must have the MSS, and thecommunication via the MSSs makes it impossible to transmit the packetdirectly, thereby reducing the communication efficiency.

SUMMARY OF THE INVENTION

The present invention therefore has an object to provide a migrationcommunication control device that is available to any apparatus employedin existing networks. Also the present invention has another object toprovide a migration communication control device that enables the mobilenode and stationary node to communicate continuously when the formermigrates by transmitting and receiving the packet directly besidestransferring the packet as has been done when the mobile node migratesacross the networks.

The above objects are fulfilled by a migration communication controldevice constructed to control a communication between a mobile node anda partner node, the mobile node migrating across networks and obtainingan address assigned on each network while the partner node being acommunication partner of the mobile node, comprising a first migrationcontrol unit a second migration control unit, a third migration controlunit, the second migration control unit being placed on the mobile nodeand the third migration control unit being placed on the partner node,wherein the first migration control unit comprises a packet transferunit for receiving a packet which was destined for an outdated addressof the mobile node, the outdated address assigned when the mobile nodemigrated to a network to which the first migration control unit isattached, generating a conversion packet which holds an updated addressinstead of the outdated address, and transmitting the conversion packet;and an address post unit for transmitting an address post message whichindicates the updated address of the mobile node to the third migrationcontrol unit, the third migration control unit transmitting the packetreceived by the packet transfer unit, and the second migration controlunit comprises a migration post unit for transmitting to the firstmigration control unit a migration post message which indicates theupdated address of the mobile node when the mobile node migrates toanother network; and a packet resumption unit for receiving theconversion packet from both the first migration control unit and thethird migration control unit and resuming an original packet from theconversion packet, and the third migration control unit comprises apacket conversion unit for converting a destination address of a packet,the packet to be transmitted to the mobile node, into the updatedaddress indicated by the address post message, the address post messagesent by the first migration control unit, and transmitting it to themobile node.

The migration post unit in the second migration control unit maytransmit an identification key included in the migration post message,the identification key being employed to identify the mobile node.

The identification key may be an address of the mobile node assigned atone network before the network to which the mobile node is currentlyattached.

The identification key may be an address of the mobile node assignedbefore its initial migration.

The second migration control unit may be constructed to transmit to thethird migration control unit the packet which has the same format as theresumed packet.

The first migration control unit may further comprise an address holdunit for holding the outdated address and the updated address bycorresponding them with each other; and an address comparison unit forcomparing the destination address of the received packet with theoutdated address, wherein the packet transfer unit generates theconversion packet and transmits it when the address comparison unitdetects that the destination address of the received packet coincideswith the outdated address.

The first migration control unit may further comprise an address holdunit for holding the outdated address and the updated address bycorresponding them with each other; and an address comparison unit forcomparing the destination address of the packet received by the packettransfer unit with the outdated address, wherein the address post unittransmits the address post message which indicates the updated addressof the mobile node to the third migration control unit, the thirdmigration control unit transmitting the packet received by the packettransfer unit, when the address comparison unit detects that thedestination address of the packet coincides with the outdated address.

The second migration control unit may further comprise an address holdunit for holding the outdated address and the updated address bycorresponding them with each other; and an address comparison unit forcomparing the updated address with the destination address of the packetreceived from one of the first migration control unit and the thirdmigration control unit, wherein the packet resumption unit resumes theoriginal packet from the conversion packet when the address comparisonunit detects that the updated address coincides with the destinationaddress of the packet received from one of the first migration controlunit and the third migration control unit.

The third migration control unit may further comprise an address holdunit for holding the outdated address and the updated address of themobile node by corresponding them with each other; and an addresscomparison unit for comparing the outdated address in the address holdunit with the destination address of the packet to be transmitted to themobile node, wherein the packet conversion unit converts the destinationaddress of the packet to be transmitted to the mobile node into theupdated address which corresponds to the outdated address in the addresshold unit when the address comparison unit detects the outdated addressin the address hold unit coincides with the destination address of thepacket.

There may be a plurality of the first migration control units, and thesecond migration control unit transmits the migration post message to atleast one of the first migration control units.

The migration post unit in the second migration control unit maytransmit the migration post message to the first migration control unitwhich is attached to the network to which the mobile node was attachedbefore its migration, each of the first migration control units has amigration post unit for transmitting to one of the other first migrationcontrol units a migration post message to post the same address as theupdated address indicated by the migration post message received fromthe second migration control unit, and each of the first migrationcontrol units has a migration post unit for transmitting a migrationpost message from one of the other first migration control units toanother first migration control unit to post the same address as theupdated address indicated by the received migration post message.

Each of the first migration control units and the second migrationcontrol unit may further comprise a pointer hold unit for holdingpointers related to the first migration control unit to which themigration post message is transmitted, and wherein the migration postunit in each of the first migration control units and the migration postunit in the second migration control unit transmit the migration postmessage to each of the addresses related to each, of the pointers.

Each of the pointers may be a broadcast address of the network to whichone of the first migration control units is attached.

Each of the pointers may be an address which is assigned to one of thefirst migration control units uniquely.

Each of the pointers may be the address of the mobile node which isassigned when the mobile node is attached to the same network as is thefirst migration control unit, and the migration post unit in the firstmigration control unit and the migration post unit in the secondmigration control unit obtain the broadcast address of the network towhich each of the first migration control units is attached withreferring to the address of the mobile node, and transmits the migrationpost message to the obtained broadcast address.

The pointer hold unit in the second migration control unit may hold apointer related to a first migration control unit for the latestmigration, which is the first migration control unit being attached toone network before the network to which the mobile node is currentlyattached, and the pointer hold unit in the first migration control unitholds a pointer related to another first migration control unit attachedto the same network as was the mobile node attached before migrating tothe network to which the first migration control unit is attached.

The second migration control unit may further transmit to the firstmigration control unit the pointer by sending thereto the migration postmessage, the pointer to be held by the first migration control unit.

The first migration control unit may store into the pointer hold unitthe pointer when it receives from the second migration control unit themigration post message by corresponding the pointer with the updatedaddress indicated by the received migration post message.

Each of the first migration control units may further comprise anaddress hold unit for holding the outdated address and the updatedaddress by corresponding them with each other, wherein a migration postmessage unit stores into the address hold unit the outdated address andthe updated address by corresponding them with each other when itreceives from the second migration control unit the migration postmessage, while converts the updated address in the address hold unitinto the updated address indicated by the migration post message when itreceives from the first migration control unit the migration postmessage and the outdated address indicated by the migration post messagecoincides with one of the updated addresses in the address hold unit.

The first migration control unit may be placed on a gateway, whichconnects networks.

The first migration control unit may be placed on the network as anindividual node.

The migration post unit in the second migration control unit maytransmit the migration post message to a home migration control unit,the home migration control unit being the first migration control unitwhich is attached to a network where the mobile node left for itsinitial migration, and the home migration control unit may furthercomprise a home migration post unit for transmitting a migration postmessage to a first migration control unit for the latest migration, thefirst migration control unit for the latest migration being the firstmigration control unit which is attached to the network where the mobilenode left for the latest migration, to post the same updated address asis indicated by the migration post message received from the secondmigration control unit.

The first migration control unit may further comprise a migration postunit for transmitting the migration post message indicating the updatedaddress of the mobile node to one of the other first migration controlunits when the conversion packet destined for the outdated address ofthe mobile node was sent therefrom to the first migration control unit.

The migration post unit in the second migration control unit maytransmit to the home migration control unit the migration post messagewhere a home address and the updated address are corresponded with eachother, the home address assigned when the mobile node is attached to thesame network as is the home migration control unit, and each of thepacket transfer unit and the address post unit in the home migrationcontrol unit may transmit the conversion packet and the address postmessage respectively with referring to the above home address and theupdated address.

The second migration control unit may further comprise an outdatedaddress post unit for transmitting to the first migration control unitfor the latest migration an outdated address post message where theoutdated address and the home address are corresponded with each other,the outdated address being assigned to the mobile node before the latestmigration, the home migration post unit in the home migration controlunit may transmit to the said first migration control unit for thelatest migration the migration post message where the above home addressand the updated address are corresponded with each other, and the packettransfer unit and the address post unit in the first migration controlunit for the latest migration may transmit the conversion packet and theaddress post message respectively in accordance with the outdatedaddress and the updated address, the outdated address and the updatedaddress being corresponded with each other via the home address.

The outdated address post unit in the second migration control unit maytransmit the above outdated address post message at a migration of themobile node preceding the latest migration, and each of the migrationpost units in the second migration control unit and the home migrationpost unit in the home migration control unit may transmit the abovemigration post message at the latest migration of the mobile node.

The second migration control unit may further comprise a home migrationcontrol unit pointer hold unit for holding a pointer related to the homemigration control unit, the migration post unit in the second migrationcontrol unit transmits the migration post message to the address relatedto the pointer, the home migration control unit may further comprise apointer hold unit for the latest migration for holding a pointer relatedto the first migration control unit for the latest migration, and thehome migration post unit in the home migration control unit may transmitthe migration post message to the address related to the pointer.

Each of the above pointers may be the broadcast address of the networkto which each of the first migration control units is attached.

Each of the above pointers may be the address assigned to each of thefirst migration control units uniquely.

The second migration control unit may further comprise a pointerobtainment unit for requesting to the first migration control unit forthe latest migration the pointer related to the first migration controlunit for the latest migration, and the migration post unit in the secondmigration control unit may post the obtained pointer to the homemigration control unit together with the updated address by sendingthereto the migration post message.

The migration post unit in the second migration control unit may post tothe home migration control unit the pointer at the migration of themobile node preceding the latest migration, while the migration postunit may post the above updated address at the latest migration of themobile node.

The first migration control unit may further comprise an address postsuppressing unit for suppressing transmission of the address postmessage from the address post unit to the third migration control unit,and the address post suppressing unit may suppress transmission of theaddress post message when none of the first migration control units isattached to the same network as is the mobile node.

The second migration control unit may further comprise a detect unit fordetecting whether or not the first migration control unit is attached tothe network to which the mobile node migrates, the migration post unitin the second migration control unit may transmit to the home migrationcontrol unit the migration post message which includes the detectingresult of the above detect unit together with the updated address, thehome migration post unit in the home migration control unit may transmitto the first migration control unit for the latest migration themigration post message which includes the detecting result of the abovedetect unit together with the updated address, and the address postsuppressing unit in each of the home migration control unit and thefirst migration control unit for the latest migration may suppress thetransmission of the address post message in accordance with thedetecting result of the above detect unit.

The first migration control unit may further comprise a packet transfersuppressing unit for suppressing transfer of the packet conducted by thepacket transfer unit.

The first migration control unit may further comprise an address postsuppressing unit for suppressing transmission of the address postmessage from the address post unit to the third migration control unit,and the address post suppressing unit in the first migration controlunit being attached to a network to which the mobile node is notattached, may suppress the transmission of the address post message whenthe packet transfer suppressing unit in the first migration control unitfor the latest migration suppresses transfer of the packet.

The second migration control unit may further comprise a detect unit fordetecting whether or not the packet transfer suppressing unit in thefirst migration control unit suppresses the transfer of the packet, thefirst migration control unit being attached to the network to which themobile node migrates, and the migration post unit in the secondmigration control unit transmits to the home migration control unit themigration post message which includes the detecting result of the abovedetect unit together with the updated address, the home migration postunit in the home migration control unit may transmit to the firstmigration control unit for the latest migration the migration postmessage which includes the detecting result of the detect unit togetherwith the updated address, and the address post suppressing unit in eachof the home migration control unit and the first migration control unitfor the latest migration may suppress the transmission of the addresspost message in accordance with the detecting result of the above detectunit.

The packet transfer suppressing unit in the first migration control unitfor the latest migration may suppress the transfer of the packetconducted by the packet transfer unit, when the packet transfersuppressing unit in the first migration control unit being attached tothe network to which the mobile node migrates suppresses the transfer ofthe packet.

The above objects may also be fulfilled by a packet transfer migrationcontrol unit in a migration communication control device, the migrationcommunication control device being constructed to control acommunication between a mobile node and a partner node, the mobile nodemigrating across networks and obtaining an address assigned on eachnetwork while the partner node being a communication partner of themobile node, comprising a packet transfer unit for receiving a packetwhich was transmitted by the partner node to an outdated address of themobile node, the outdated address being assigned when the mobile nodemigrated to a network to which the packet transfer migration controlunit is attached, generating a conversion packet which holds an updatedaddress instead of the outdated address, and transmitting the conversionpacket; and an address post unit for transmitting an address postmessage which indicates the updated address of the mobile node to thepartner node, the partner node transmitting the packet received by thepacket transfer unit.

The above objects may further be fulfilled by a mobile node migrationcontrol unit in a migration communication control device, the migrationcommunication control device being constructed to control acommunication between a mobile node which migrates across networks andobtains an address assigned on each network and a partner node which isa communication partner of the mobile node, being placed on the mobilenode and comprising a migration post unit for transmitting to a packettransfer migration control unit a migration post message which indicatesan updated address of the mobile node when the mobile node migrates toanother network, the packet transfer migration control unit forreceiving a packet which was transmitted by the partner node to anoutdated address of the mobile node, the outdated address assigned whenthe mobile node migrated to a network to which the migration controlunit for packet transfer is attached, generating a conversion packetwhich holds the updated address instead of the outdated address, andtransmitting the conversion packet; and a packet resumption unit forreceiving the conversion packet from both the packet transfer migrationcontrol unit and the mobile node, and resuming an original packet fromthe conversion packet.

The above objects are finally fulfilled by a partner node migrationcontrol unit in a migration communication control device, the migrationcommunication control device being constructed to control acommunication between a mobile node which migrates across networks andobtains an address assigned on each network and a partner node which isa communication partner of the mobile node, being placed on the mobilenode and comprising an address post message receiving unit for receivingan address post message which indicates an updated address of the mobilenode from a packet transfer migration control unit, the packet transfermigration control unit transmitting an address post message whichindicates the updated address of the mobile node to the partner node;and a packet conversion unit for converting a destination address of apacket, the packet to be transmitted to the mobile node, into theupdated address indicated by the address post message, and transmittingit to the mobile node.

According to the above construction, the migration communication controldevice of the present invention transfers and converts the packet usingthe address assigned to the mobile node each time it migrates acrossnetworks, obviating particular addresses or devices such as the VIPaddress used conventionally. For this reason, the migrationcommunication control device of the present invention can be applied tothe existing partner node and mobile node so that they can communicatecontinuously by transferring the packet. Moreover, it is advantageousthat the migration communication control device of the present inventionis not necessarily applied to all the nodes to enhance communicationefficiency; the present invention can be applied only to where necessaryon the existing networks. More precisely, when any existing partner nodecommunicates with the mobile node when it migrates, the packet can betransmitted directly from the mobile nodes to the existing partner node;and it can be transferred via the first migration control unit from theexisting partner node to the mobile node, thereby enhancingcommunication efficiency.

Furthermore, when the partner node employs the migration communicationcontrol device of the present invention, communication efficiency isfurther enhanced thanks to the direct packet transmission and receptionmade possible by posting the update address of the mobile node from thefirst migration control unit to the third migration control unit.

Also, the devices such as MSS or a gateway employing the VIP are notnecessarily installed at every network to which the mobile nodemigrates. To be precise, according to the present invention, thecontinuous communication is implemented even when the mobile nodemigrates to a network at which no special devices including above onesare installed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and the other objects, advantages and features of the inventionwill become apparent from the following description thereof taken inconjunction with the accompanying drawings which illustrate a specificembodiment of the invention. In the drawings:

FIG. 1 is a block diagram depicting a construction of a migrationcommunication control device in a first embodiment of the presentinvention;

FIG. 2 is a block diagram depicting a detailed construction of themigration communication control device employed as a mobile node in thefirst embodiment of the present invention;

FIG. 3 is a block diagram depicting a detailed construction of themigration communication control device employed as a gateway in thefirst embodiment of the present invention;

FIG. 4 is a block diagram showing a detailed construction of themigration communication control device employed as a stationary node inthe first embodiment of the present invention;

FIG. 5 is a block diagram showing a detailed construction of themigration communication control device employed as a n individual nodein the first embodiment of the present invention;

FIG. 6 is an illustration showing a first example of a network to whichthe migration communication control devices in FIGS. 2, 3, 4 areattached;

FIGS. 7a, 7 b, and 7 c are illustrations showing a second example of thenetwork to which the migration communication control devices in FIGS. 2,3, 4 are attached;

FIG. 8 is an illustration showing a third example of the network towhich the migration communication control devices in FIGS. 2, 3, 4 areattached;

FIGS. 9a, 9 b, and 9 c are illustrations showing a fourth example of thenetwork to which the migration communication control devices in FIGS. 2,3, 4 are attached;

FIGS. 10a and 10 b are illustrations showing (a) data in a data holdunit 1 in the mobile node (b) data in a data hold unit 1 in themigration communication control devices each employed as the gateway,the stationary node, and the individual node;

FIGS. 11a-11 f are illustrations showing a format of a packet in thefirst embodiment of the present invention;

FIGS. 12a-12 e are illustrations showing a format of a packet in thefirst embodiment of the present invention;

FIGS. 13a-13 c are illustrations showing a content of the data hold unit1 in the migration communication control device employed as the gateway;

FIGS. 14a-14 c are illustrations showing a content of the data hold unit1 in the migration communication control device employed as theindividual node;

FIG. 15 is an illustration showing an example of a network to which themigration communication control device is attached in a secondembodiment of the present invention;

FIG. 16 is a detailed block diagram depicting a home migrationcommunication control device in the second embodiment of the presentinvention;

FIG. 17 is an illustration showing a content of a home mobile host listhold unit in the second embodiment of the present invention;

FIG. 18 is a detailed block diagram depicting the visitor migrationcommunication control device in the second embodiment of the presentinvention;

FIG. 19 is an illustration showing a content of a visitor mobile hostlist hold unit in the second embodiment of the present invention;

FIG. 20 is a detailed block diagram depicting a migration address unitin the second embodiment of the present invention;

FIG. 21 is an illustration showing a content of an address hold unit inthe migration address unit in the second embodiment of the presentinvention;

FIG. 22 is a detailed block diagram depicting a migration address unitin the second embodiment of the present invention;

FIG. 23 is an illustration showing a content of the address hold unit inthe migration address unit in the second embodiment of the presentinvention;

FIGS. 24a-24 c are illustrations showing a format of a data packet inthe second embodiment of the present invention;

FIG. 25 is an illustration showing a format of a packet transfer messagein the second embodiment of the present invention;

FIG. 26 is an illustration showing a flow of a data packet transmittedbetween devices in the second embodiment of the present invention;

FIG. 27 is an illustration showing a communication sequence in FIG. 26;

FIGS. 28A-28F are illustrations showing a construction of each datapacket in FIG. 26;

FIG. 29 is an illustration showing a change in the content of each holdunit in FIG. 26;

FIG. 30 is an illustration showing a flow of each data packettransmitted between devices at an operation example in the secondembodiment of the present invention;

FIG. 31 is an illustration showing a communication sequence in FIG. 30;

FIGS. 32A-32E are illustrations showing a construction of each datapacket in FIG. 30;

FIG. 33 is an illustration showing a change in the address hold unit ineach device in FIG. 33;

FIG. 34 is an illustration showing a flow of a data packet transmittedbetween devices at an operation example in the second embodiment of thepresent invention;

FIG. 35 is an illustration showing the communication sequence in FIG.34;

FIGS. 36A-36H are illustrations showing a construction of each datapacket in FIG. 34;

FIG. 37 is an illustration showing a change in the address hold unit ineach device in FIG. 34;

FIG. 38 is an illustration showing a flow of each data packettransmitted between devices at an operation example in the secondembodiment of the present invention;

FIG. 39 is an illustration showing a communication sequence in FIG. 38;

FIGS. 40A-40E are illustrations showing a construction of each datapacket in FIG. 38;

FIG. 41 is an illustration showing a change in the address hold unit ineach device in FIG. 38;

FIG. 42 is an illustration showing a flow of each data packettransmitted between devices in the second embodiment of the presentinvention;

FIG. 43 is an illustration showing a flow of each data packettransmitted between devices in the second embodiment of the presentinvention;

FIG. 44 is an illustration showing a flow of each data packettransmitted between devices in the second embodiment of the presentinvention; and

FIG. 45 is an illustration showing a flow of each data packettransmitted between devices in the second embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[Embodiment 1]

A construction of a migration communication control device in a firstembodiment of the present invention is described hereunder withreferring to FIGS. Hereinafter, the mobile node and partner node in therelated art as well as in the summary of the invention are referred toas a mobile host and a stationary host, respectively.

FIG. 1 is an illustration showing the construction of the migrationcommunication control device comprising a data hold unit 1, anapplication unit 2, a migration address unit 3, and a communicationcontrol unit 4.

The data hold unit 1 holds a couple of addresses of a mobile host bycorresponding them. Each of the addresses in the data hold unit 1 isassigned before and after a migration of the mobile host.

The application unit 2 checks a connection as well as monitors a timer.The unit 2 is relevant for a higher layer in OSI model, which includesan application layer. For example, the unit 2 operates as TCP at TCP/IP(Transmission Control Protocol/Internet Protocol) or a layer which ishigher than TCP.

The migration address unit 3 processes a migration address withreferring to data in the data hold unit 1. The concrete operation of themigration address unit 3 varies depending on a type of the migrationcommunication control device comprising the unit 3, and this will bedescribed in detail later.

The communication control unit 4 controls the communication. The unit 4is relevant for a lower layer in the OSI model. For example, the unit 4operates as a layer which is lower than IP at TCP.

The application unit 2 and the communication control unit 4 are the sameunits as ones implemented on a general host. Besides the unit 2 and 4,the migration communication device in the first embodiment of thepresent invention includes the data hold unit 1 and the migrationaddress unit 3; thereby implements an operation unique to this case.That is, the data hold unit 1 and the migration address processing unit3 are attached to the mobile host which migrates across networks, or astationary host which is attached to a network fixedly (for example, agateway or a server); otherwise, they operate alone. Each devicecomprising the unit 1 and 3 supports a continuous communicationunaffected by migration of the mobile host besides providing its ownfunction.

The data hold unit 1 and the mobile address unit 3, which are includedin the devices attached to the network, are described in FIGS. 2, 3, 4,5. FIG. 2 shows a migration communication control device where the unit1 and the unit 3 are attached to the mobile host which migrates acrossnetworks; FIG. 3 shows a migration communication control device wherethe unit 1 and the unit 3 are attached to a gateway which connects thenetworks; FIG. 4 shows a migration communication control device wherethe unit 1 and the unit 3 are attached to the stationary host, which isthe communication partner of the mobile host; and FIG. 5 shows amigration communication control device attached to the network itself.

The migration communication control device in FIG. 2 (hereinafterreferred to as a mobile host) further includes the application unit 2,the communication control unit 4, and an address obtainment unit 25,besides the data hold unit 1 and the migration address unit 3.

Each of the application unit 2 and the communication control unit 4operates as the above; while the unit 2 together with the unit 4 operateas a conventional stationary host.

The address obtainment unit 25 obtains an address of the mobile hostassigned when it has migrated to another network. Although other optionscan be considered, such as employing a manual setting by an operator orcommunicating with a server computer which administrates addresses ofthe network, it is supposed here that the address is obtained inaccordance with an instruction of a system administrator or theoperator. The address obtainment unit 25 is also possessed by a generalhost and will not be described in detail.

The addresses held in the data hold unit 1 are obtained by the addressobtainment unit 25.

The migration address unit 3 (enclosed with a broken line) consists of aresponse message transmission unit 20, a marked packet conversion unit21, a migration address setting unit 26, a migration post transmissionunit 27, a reception packet unit 28, and a marked packet resumption unit29.

The response message transmission unit 20 transmits the packet whichresponds to the received packet if the response is needed.

The marked packet conversion unit 21 converts a packet received from theresponse message transmission unit 20 as well as the application unit 2into a marked packet by converting the address of the received packetand marking the packet.

The migration address setting unit 26 stores the address obtained by theaddress obtainment unit 25 into the data hold unit 1. The addressobtained by the unit 25 is the address of the mobile host assigned afterthe migration, and the unit 26 stores it into unit 1 by corresponding itto the address of the mobile host assigned before the migration.

The migration post transmission unit 27 posts via the communicationcontrol unit 4 that the address obtained by the unit 25 is held in thedata hold unit 1 together with the correspondence between a coupleaddresses each of which assigned before and after the migration.

The reception packet unit 28 detects whether or not the received packetis marked, and sends the unmarked packet to the application unit 2 whilesending the marked packet to the marketed packet resumption unit 29.

The marked packet resumption unit 29 resumes the marked packet.

The migration communication control device in FIG. 3 (hereinafterreferred to as a gateway) further includes the application unit 2 andthe communication control unit 4 besides the data hold unit 1 and themigration address unit 3 (enclosed with a broken line).

Each of the application unit 2 and the communication control unit 4operates described the above, and the unit 2 together with the unit 4operate as a conventional gateway.

The data hold unit 1 holds the correspondence between a couple of theaddresses of the mobile host each of which assigned before and aftermigration.

The migration address unit 3 consists of a reception packet unit 35, amigration post information unit 36, an address comparison unit 37, anaddress conversion post transmission unit 38, and a marked packetconversion unit 39.

The reception packet unit 35 detects whether or not the received packetis the packet comprising a migration post message, which is transmittedby the mobile host. The unit 35 then sends the migration post message tothe migration post information unit 36 while sending the other packetsto the address comparison unit 37.

In accordance with the migration post message received from thereception packet unit 35, the migration post information unit 36 storesin the data hold unit 1 the correspondence between a couple of theaddresses of the mobile host each of which assigned before and after themigration. The unit 36 also sends the migration post message to theaddress conversion post transmission unit 38.

The address comparison unit 37 detects whether or not the destinationaddress of the packet received from the reception packet unit 35coincides with the address of the mobile host assigned before migration,which is held in the data hold unit 1. When they coincide with eachother, the unit 37 further sends to the marked packet conversion unit 39the address assigned after the migration, which corresponds to theaddress which coincides with the destination address, as well as thepacket received from the reception packet unit 35. On the other hand,when they do not coincided with each other, the unit 37 implements afunction of a gateway by sending the packet to the application unit 2.

The address conversion post transmission unit 38 transmits to thedestination address of the above packet received from the receptionpacket unit 35 an address conversion post message to inform that theaddress of the mobile host changes when the address comparison unit 37detects a coincidence. Also the unit 38 transmits the address conversionpost message to the network which satisfies the following twoconditions: (1) the network where the address assigned before themigration, which is held in the data hold unit 1, is other than 0 (2)the migration communication control device employs as the gateway is notattached to the network. When the address conversion post message istransmitted to the network, which satisfies the above conditions, itsdestination address is a broadcast address of the network. The broadcastaddress consists of a network part and a host part, and every bit of thehost part is 1.

The marked packet conversion unit 39 generates a marked packet when theaddress comparison unit 37 detects a coincidence. The unit 39 generatesit by marking a general packet after converting the destination addressof the packet. Then, the unit 39 transmits it.

The migration communication control device in FIG. 4 (hereinafterreferred to as a stationary host) further includes the application unit2 and the communication control unit 4 besides the data hold unit 1 andthe migration address unit 3 (enclosed with a broken line).

Each of the application unit 2 and the communication control unit 4operates as described the above, and the unit 2 together with the unit 4operate as a conventional stationary host (not migrate).

The data hold unit 1 holds the correspondence between a couple of theaddresses of the mobile host each of which assigned before and after themigration.

The migration address unit 3 consists of a reception packet unit 45, amarked packet resumption unit 46, an address conversion post informationunit 47, an address comparison unit 48, and a marked packet conversionunit 49.

The reception packet unit 45 detects whether the received packet is thepacket comprising the address conversion post message, the markedpacket, or the other packets. The address conversion post message istransmitted by the gateway. Then the unit 45 sends the addressconversion post message to the address conversion post information unit47, the marked packet to the marked packet resumption unit 46, and theother packets to the application unit 2.

The marked packet resumption unit 46 resumes the unmarked packet fromthe marked packet, which is received from the reception packet unit 45.

The address conversion post information unit 47 obtains from the packetcomprising the address conversions post message, which is received fromthe reception packet unit 45, the correspondence between the address ofthe mobile host assigned before the migration and the one assigned afterthe migration, and stores it into the data hold unit 1.

The address comparison unit 48 detects whether or not destinationaddress of the packet received from the application unit 2 coincideswith the address of the mobile host assigned before migration, which isheld in the data hold unit 1. When they coincide with each other, theunit 48 further sends to the marked packet conversion unit 49 theaddress assigned after the migration, which corresponds to the addresswhich coincides with the destination address, as well as the packetreceived from the application unit 2. On the other hand, when they donot coincided with each other, the unit 48 sends the packet to thecommunication control unit 4.

The marked packet conversion unit 49 generates a marked packet when theaddress comparison unit 37 detects a coincidence. The unit 49 generatesit by marking a general packet after converting the destination addressof the packet. Then, the unit 49 transmits it.

The migration communication control device in FIG. 5, which is attachedto the network by itself, consists of the data hold unit 1, themigration address unit 3 (enclosed with a broken line), and thecommunication control unit 4.

The data hold unit 1 holds the correspondence between a couple of theaddresses of the mobile host each of which assigned before and after themigration.

The migration address unit 3 consists of the reception packet unit 35,the migration post information unit 36, the address comparison unit 37,the address conversion post transmission unit 38, and the marked packetconversion unit 39. The units integrating the migration address unit 3operate substantially same as equivalent units integrating the gatewayin FIG. 3 except the following.

In FIG. 3 the address conversion post transmission unit 38 transmits theaddress conversion post message to the network satisfying both of thetwo conditions, which are described in the above; whereas, the addressconversion post transmission unit 38 in FIG. 5 transmits the addressconversion post message to the broadcast address of the network as longas the network satisfies the first condition, that is it transmits theaddress conversion post message to the network when the address assignedbefore the migration, which is held in the data hold unit 1, is otherthan 0.

FIG. 6 shows a first example of a network to which the migrationcommunication control device as the mobile host in FIG. 2, the migrationcommunication control device as the gateway in FIG. 3, and migrationcommunication control device as the stationary host in FIG. 4 areattached. In the figure numeral 11 denotes a mobile host in FIG. 2,which migrates from a network A to a network B and obtains an address αassigned on the network A as well as an address β assigned on thenetwork B.

Numeral 12 denotes a stationary host in FIG. 3, which is attached to thenetwork B and obtains an address γ assigned thereon.

Numeral 12′ denotes a stationary host in FIG. 3, which is attached tothe network A and obtains an address γ′ assigned thereon.

Numeral 13 denotes a gateway in FIG. 3, which has an address g. Thegateway 13 is attached to both the network A and the network B.

The address on each network is assigned by a system administrator.

FIGS. 7a-7 c show a second example of a network to which the mobile hostin FIG. 2, the gateway in FIG. 3, and the stationary host in FIG. 4 areattached. The stationary host is not illustrated in FIGS. 7a-7 c sinceits location does not affect the communication with the mobile host.

In the figure the mobile host 11 migrates across network 1-4, andobtains an address m, m′, m″, m′″ assigned on each network respectively.

The network 5 as well as each of the network 1-4 (hereinafter referredto as the net 5, and the net 1-4 respectively) are connected with eachother by a gateway 14, as shown in the figure.

A gateway 1-4 (hereinafter referred to as gw 1-gw 4) is the migrationcommunication control device employed as the gateway in FIG. 3.

FIG. 8 shows a third example of the network to which the mobile host, inFIG. 2, the gateway in FIG. 3, and the stationary host in FIG. 4 areattached. Construction of this network is substantially same as thesecond example of the network in FIG. 6 although operation thereof isdifferent from the second example, which will be described later.

FIGS. 9a-9 c show a fourth example of the network to which the mobilehost in FIG. 2, the migration communication control device in FIG. 5,the stationary host in FIG. 4 are attached. The migration communicationcontrol device as the stationary host will not be described here.

In the figure, numeral 11 denotes the mobile host which migrates acrossthe network 1-4 and obtains the address m, m′, m″, m′″ assigned on eachnetwork respectively.

The network 5 as well as each of the network 1-4 (hereinafter referredto as the net 5, and the net 1-4 respectively) are connected with eachother by a gw 1-4, as shown in the figure.

Each of the migration communication control unit 1-4 (hereinafterreferred to as S1-S4) is relevant for the one in the FIG. 5.

An address used in the first embodiment of the present invention isdescribed hereunder. Each address consists of a network part, which isassigned on each network and shared by every host attached to thatnetwork, as well as a host part, which is assigned to each hostuniquely.

A broadcast address is a special kind of address, which can be dividedinto two types. The first one is the broadcast address used as thedestination address in transmitting a packet from a network to anothernetwork, such as the broadcast address where every bit of the host partis 1. When the first type of the broadcast address is used as thedestination address of the packet, the packet is transferred by thegateway to the network directed by the network part of the broadcastaddress. The other one is used in transmitting a packet within anetwork, such as the broadcast address where every bit of both the hostpart and the network part is 1. When the second type of the broadcastaddress is used as the destination address of the packet, the packet istransmitted to all the devices attached to the network, which includesthe broadcast address. However, the gateway does not transfer the packetto any other network.

Operations of the migration communication control device in the firstembodiment of the present invention are described hereunder withreferring to drawings.

(Operation Example in FIG. 6)

In FIG. 6, when the mobile host migrates from the network A to thenetwork B, the migration communication control device is operated asfollows.

In a first operation, the mobile host and the gateway operate when themobile host migrates across networks.

In a second operation, the stationary host transmits a packet to anaddress of the mobile host which was assigned before the migration.

In a third operation, the stationary host transmits the packet to anaddress of the mobile host which has been assigned after the migration.

In a fourth operation, the mobile host receives the packet which istransmitted by the stationary host.

In a fifth operation, the mobile host sends a response message to thestationary host.

(First Operation in FIG. 6)

In FIG. 6 the mobile host 11 attached to the network A (enclosed with abroken line) migrates to the network B to complete ongoing communicationwith the stationary host 12, which is attached to the network B. Whenmigrating to the network B, the address obtainment unit 25 in the mobilehost 11 (FIG. 2) obtains the address β assigned on the network B.

Immediately after obtaining the address β, the address obtainment unit25 gives the address β to the migration address setting unit 26 and themigration post transmission unit 27. The migration address setting unit26 stores the address β into the data hold unit 1 by corresponding it tothe address α, which is the address assigned before the migration. FIG.10(a) shows the content of the data hold unit 1. The migration posttransmission unit 27 gives to the gateway 13 via the communicationcontrol unit 4 a packet comprising migration post message and thecorrespondence between the address α and the address β, so that thegateway 13 will know that the mobile host 11 has migrated to the networkB. The mobile host 11 can transmit the packet both before and after themigration. In FIG. 6 a packet 51 is transmitted before the migration,and its format is shown in FIG. 11(a). As shown in FIG. 11(a), thepacket 51 consists of a destination address 91, a source address 92, anddata 93. The data 93 further comprise a message type 98, an addressbefore migration 94, and an address after migration 95.

Receiving from the communication control unit 4 the packet 51, the gateway 13 sends it to the reception packet unit 35, the unit 4 and the unit35 being in FIG. 3. From the message type 98 in FIG. 11(a), the gateway13 identifies the packet 51 with the migration post message, and givesthe packet 51 to the migration post information unit 36. The migrationpost information unit 36 obtains from the data 93 in the data packet 51the address before migration α and the address after the migration β;then stores them into the data hold unit 1 by corresponding them witheach other. The content of the data in the data hold unit 1 is shown inFIG. 10(b).

Additionally, the destination address 91 of the packet in FIG. 11(a),can be the broadcast address of the network A, where the network partnames the network A and every bit of the host part is 1. When thebroadcast address is employed, every stationary host attached to thenetwork A, including the gate way 13, receives the correspondence of theaddresses each of which assigned before and after the migration. In thiscase communication control unit 4 in the stationary host 12′ receivesthe data packet 51, and gives it to the reception packet unit 45, theunit 4 and the unit 45 in FIG. 4. From the message type 98 in FIG.11(a), the reception packet unit 45 identifies the packet 51 with themigration post message, and gives the packet 51 to the addressconversion post information unit 47. The unit 47 obtains from the data93 in the data packet 51 the address before migration a and the addressafter the migration β and stores them into the data hold unit 1 bycorresponding them with each other. Once those addresses are stored inthe data hold unit 1, the stationary host 12′ can transmit a packet tothe address assigned after the migration instead of transmitting it tothe address before the migration, the same to other stationary hostsattached to the network A.

(Second Operation in FIG. 6)

In the second operation, the stationary host 12 transmits a packet tothe address assigned before the migration after the mobile host 11migrates to the network B and obtains the address β assigned on thenetwork B. It is supposed that the mobile host 11 transmits the packet51, which comprises the migration post message, to the gateway 13 ratherthan to the broadcast address of the network A.

The stationary host 12, which is not notified that the mobile host 11has migrated to the network B, transmits the packet to the address α ofthe mobile host, which was assigned before the migration. A packet 52 inFIG. 6 is transmitted by the stationary host 12 to the address α of themobile host 11, and its format is shown in FIG. 11(f). The packet 52 isreceived by the gateway 13. Because the gateway 13 is located betweenthe source address of the packet 52 and the address of the mobile host aassigned before the migration, and also it is attached to the network A,to which the mobile host 11 was attached before the migration.

The gateway 13 employs its devices in FIG. 3 to implement its functionsincluding reception of the packet. That is, the communication controlunit 4 in the gateway 13 receives the packet 52, and sends it to thereception packet unit 35 in the migration address unit 3. The receptionpacket unit 35 identifies the packet 52 with a general packet and givesit to the address comparison unit 37. The unit 37 compares thedestination address α of the packet 52 with the address before themigration, which is held in the data hold unit 1; then detects whetheror not they are coincide with each other. When the destination addressof the received packet does not coincide with the address assignedbefore the migration, the address comparison unit 37 sends the packet tothe application unit 2. On the other hand, when they coincide with eachother, the address comparison unit 37 obtains from the data hold unit 1the address β of the mobile host assigned after the migration, whichcorresponds to the address α; then sends it both to the addressconversion post transmission unit 38 and the marked packet conversionunit 39.

As is described the above, the packet 52 is transmitted to the address αof the mobile host 11 by the stationary host 12. Therefore, the addressconversion post transmission unit 38 notifies the stationary host 12that the address of the mobile host 11 has changed by transmittingthereto the packet 53. FIG. 11(b) shows the packet 53. Simultaneously,the marked packet conversion unit 39 converts the packet 52 into thepacket 53 by rewriting the destination address of the packet 52 to theaddress β assigned after the migration, returning thereto the previousdestination address of the packet 52 as additional information, andmarking to show that its destination address has changed; then sends thepacket to the communication control unit 4. Thereby, the packet 52,which is converted into the marked packet 52′, is transferred from theaddress α of the mobile host 11 assigned before the migration to theaddress β assigned after the migration. FIG. 12(e) shows the packet 52′.

Receiving the packet 53 from the communication control unit 4 in thestationary host 12, it sends its packet 53 to the reception packet unit45, the unit 4 and the unit 45 being in FIG. 4. From the message type 98in FIG. 11(b), the reception packet unit 45 identifies the packet 53with the address conversion post message, and gives the packet 53 to theaddress conversion post information unit 47. The address conversion postinformation unit 47 obtains from the data 93 in the data packet 53 theaddress before migration α and the address after the migration β; thenstores them into the data hold unit 1 by corresponding them with eachother. Thereby, the stationary host 12 obtains the address of the mobilehost 11 assigned after the migration, so that a direct communicationbetween the stationary host 12 and the mobile host 11 is implemented.

In the second operation the migration communication control devicecomprising the units in FIG. 4 is employed as the stationary host 12.However, a conventional stationary host, which is not constructed as themigration communication control device can also be communication partnerof the mobile host if it is attached to a network. Therefore, hereundera communication between the mobile host 11 and the convention stationaryhost is described.

When the conventional stationary host transmits a packet to the addressof the mobile host 11 assigned before the migration after the mobilehost 11 has migrated to another network, the gateway 13 transfers thepacket to the address of the mobile host 11 assigned after the migrationas well as sends to the stationary host the packet 53 comprising theaddress conversion post message in FIG. 11(c). This operation is same asthe above.

However, when receiving the packet 53, the stationary host disposes itsince it does not support the address conversion post message and judgesthe packet 53 is not a required packet. Thus, the conventionalstationary host cannot utilize the packet 53 to detect the address ofthe mobile host assigned after the migration nor hold the correspondenceof the addresses each assigned before and after the migration.

Therefore, the stationary host gives the packet only to the address ofthe mobile host 11 assigned before the migration. Then, the gatewaytransfers the packet to the address of the mobile host 11 assigned afterthe migration, and the mobile host 11 receives the packet. The messagefrom the mobile host 11, such as the response message, is transmitted tothe stationary host directly, so that it is received by the stationaryhost without fail.

Thus, the conventional stationary host transmits a packet to the mobilehost indirectly and receives a packet from the mobile host directly.Continuous communication unaffected by the mobile host's migration canbe implemented, even when the conventional stationary host is employed.

(Third Operation in FIG. 6)

In the third operation, the stationary host 12 transmits the packet tothe address β of the mobile host 11 assigned after the migration withreferring to the correspondence of the addresses each assigned beforeand after the migration, which is held in the data hold unit 1. Thethird operation is described hereunder with referring to FIG. 4.

The stationary host 12 employs its devices in FIG. 4 to implementconversion of the destination address and the transmission of thepacket, both of which integrate the third operation. That is,application unit 2 sends to the address comparison unit 48 the packet54, whose destination address is the address α of the mobile host 11assigned before the migration. FIG. 11(f) shows a format of the packet54. Then, the comparison unit 48 obtains the destination address of thepacket 54 and detects whether or not it coincides with the addressbefore the migration, which is held in the data hold unit 1.

The comparison unit 48 sends the packet 54 to the communication controlunit 4 when the above addresses do not coincide with each other while itsends the packet 54 to the marked packet conversion unit 49 when theabove addresses coincide with each other. In the third operation thecoincidence is detected since the corresponded between the address α andthe address β is stored in the data hold unit 1. Therefore, the packet54 is sent to the marked packet conversion unit 49. Then the markedpacket conversion unit 49 obtains from the data hold unit 1 the addressβ of the mobile host assigned after the migration, which corresponds tothe address α as well as converts the packet 54 into the packet 54′ byconverting the destination address α into the address β, returningthereto the original destination address α as additional information,and marking the packet 54 to show that its destination address haschanged; then sends the packet 54′ to the communication control unit 4.FIG. 11(c) shows a format of the packet 54′. Since the destinationaddress of the packet 54′ is an updated address of the mobile host 11,the packet 54′ is given to the mobile host 11 without fail.

(Fourth Operation in FIG. 6)

In the fourth operation, the mobile host 11 receives the marked packet54′ and obtains the original unmarked packet 54 by resuming the packet54′. This operation is described hereunder with referring to FIG. 2.

The mobile host 11 employs its devices in FIG. 2 to implement itsoperation. That is, the communication control unit 4 receives the packet54′ and sends it to the reception packet unit 28. The reception packetunit 28 detects that the received packet 54′ is marked, and sends it tothe marked packet resumption unit 29. The unit 29 obtains the originaldestination address α, which is held in the additional information 97,and replaces the current destination address β of the packet 54′ withthe address α. Then it sends the packet 54′ to the application unit 2.Thus, the mobile host 11 can receive the packet destined for itsoutdated address.

(Fifth Operation in FIG. 6)

In the fifth operation, the mobile host 11 sends to the stationary host12 a packet comprising a response message (hereinafter referred to as aresponse packet) or a packet excluding the response message (hereinafterreferred to as a non-response packet). A type of the received packetdetermines whether or not it is responded with the response packet.

When the packet 54′ is responded with a response packet, the mobile host11 employs its devices in FIG. 2 to send the response packet. That is,the response message transmission unit 20 builds the response packet,and sends it to the marked packet conversion unit 21 together with thedestination address α of the packet 54′.

The mobile host 12 also employs its devices to send the non-responsepacket 55. That is, the application unit 2 gives the address α assignedbefore the migration and the non-response packet to the marked packetconversion unit 21. The unit 21 sends the received packet to thestationary host 12 via the communication control unit 4 without markingit. FIG. 11(e) shows the packet sent by the unit 21 to the stationaryhost 12.

The communication control unit 4 in the stationary host 4 receives thepacket 55, and gives it to the reception packet unit 45. The unit 45detects that the packet 55 is the non-response packet, so that it givesthe packet 55 to the application unit 2. Thus, the stationary host andthe mobile host implement a continuous communication unaffected bymobile host's migration. Although the migration communication controldevice is employed as the stationary host 12 in this embodiment, theconventional host can also be employed to transmit the non-responsepacket.

In the above, the unmarked response packet and the unmarked non-responsepacket are sent to the mobile stationary host 12. On the other hand,hereunder the operation of the mobile host 11 at conversion of theresponse packet and the non-response packet into the marked ones isdescribed. This will be employed effectively in a communication betweenmobile hosts.

Receiving the unmarked packet from the application unit 2, the markedpacket conversion unit 21 generates a packet 55′ where the destinationaddress and the source address are the address γ of the stationary host12 and the address β assigned after the migration respectively. Also ingenerating the packet 55′, the application unit 2 gives to the receivedpacket the address α assigned before the migration as additionalinformation as well as marks the received packet to indicate that thedestination address has converted. FIG. 11(d) shows a format of thepacket 55′. Then the application unit 2 sends the packet 55′ to thestationary host 12 via the communication control unit 4.

The communication control unit 4 in the stationary host 12 receives thepacket 55′, and sends it to the reception packet unit 45. Detecting thepacket 55′ is the marked packet, the reception packet unit 45 sends itto the marked packet resumption unit 46. The unit 46 resumes the packet55′ into the packet 55 by unmarking it and replacing the source addressthereof with the address α assigned before the migration, which is heldas the additional information. A format of the packet 55 is shown inFIG. 11(e). Thus, the stationary host and the mobile host implement acontinuous communication unaffected by mobile host's migration.

(Operation Example in FIGS. 7a-7 c)

In FIGS. 7a-7 c, when the mobile host migrates across the network 1, 2,3, and 4, and obtains a temporary address assigned on each network, thenewest address of the mobile host is transmitted to the stationary host,which operates as communication partner.

(Migration from Network 1 to Network 2)

The address of the mobile host is m when it is attached to the network1. When migrating from the network 1 to the network 2, the mobile host11 replaces its address with m′ assigned on the network 2. Then themobile host 11 notifies the migration communication control deviceattached to the network 1 that it has migrated to the network 2 bysending thereto a packet comprising a migration post message. In FIGS.7a-7 c, the migration communication control device gw 1, gw 2 attachedto the network 1 receive the migration post packet 61, and store it intoits own data hold unit 1. The operation in FIGS. 7a-7 c is substantiallythe same as the operation in FIG. 6 except that in FIGS. 7a-7 c, thepacket 61 holds the address of the mobile host assigned before the lastmigration besides the correspondence of the addresses each assignedbefore and after the current migration. The address assigned before thelast migration makes the gws prepare for further migration of the mobilehost, which will be described later. A format of the packet 61 is shownin FIG. 12a. Since the migration from the network 1 to the network 2 isthe first migration in FIGS. 7a-7 c, the packet 61 holds 0 at theaddress assigned before the last migration.

The gw 1 and the gw 2 store in the data hold unit 1 the correspondenceof the addresses each assigned before and after the migration, as wellas the address assigned before the last migration. As shown in FIG.13(a), m-m′ and 0 are stored in the data hold unit 1 of each of the gw 1and the gw 2.

Then, the gw 1 and the gw 2 detects from 0 at the address assignedbefore the last migration that no migration had been conducted beforethe current migration.

The broadcast address of the network 1 can be employed as thedestination address of the migration post packet 61. If the packet isdestined for the broadcast address, every host attached to the network1, which includes the gw 1 and the gw 2, will hold the correspondence ofthe addresses each of which assigned before and after the migration aswell as the address assigned before the last migration. Thereby, thehosts attached to the network 1 can communicated with the mobile hostdirectly.

(Migration from Network 2 to Network 3)

When migrating from the network 2 to the network 3, the mobile host 11obtains m″ at the address assigned after the migration. Then the mobilehost 11 notifies the gw 2 and a gw 3, both of which are attached to thenetwork 2, that the mobile host 11 has migrated to the network 3 bytransmitting thereto a packet comprising the migration post message,referred to as a packet 62 in FIG. 7b. FIG. 12b shows a format of thepacket 62, which is transmitted to the gw 2. The broadcast address ofthe network 2 can be employed as the destination address of the packet62. When the packet 62 is transmitted to the broadcast address of thenetwork 2, every host attached to the network 2, which includes the gw 2and the gw 3, holds the correspondence of the addresses each assignedbefore and after the migration.

The gw 2 employs its devices in FIG. 3 to process the packet 62. Thatis, receiving the packet 62, the gw 2 sends it to the migration postinformation unit 36 via the communication control unit 4 and thereception packet unit 35, then refers to the data hold unit 1 where m→m′and 0 are still held at the address correspondence and at the addressassigned before the last migration respectively. The migration postinformation post unit 36 obtains from the packet 62 m′-m″ as the newlyassigned correspondence between the addresses each of which assignedbefore and after the current migration, the migration from the network 2to the network 3. Then, it detects whether or not the address m′coincides with the address held in the data hold unit 1 as the addressassigned after the last migration. Since the unit 36 detects thecoincidence, it replaces the address m′ in the unit 1 with the addressm″ as well as replaces the correspondence m-m′ with the correspondencem-m″.

Also the migration post information unit 36 sends to the data hold unit1 the address m assigned before the last migration together with theaddress correspondence m′-m″ obtained from the current migration. Nowthe data hold unit 1 in the gw 2 holds the address m at the addressassigned before the last migration and the address correspondence m′-m″at the correspondence of the addresses each of which assigned before andafter the migration as well as the address 0 at the address assignedbefore the last migration as well as the address correspondence m-m′ atthe correspondence of the addresses each of which assigned before andafter the migration. After updating as well as adding the addresses inthe data hold unit 1, the migration post information unit 36 sends tothe address conversions post transmission unit 38 m′-m″ as the newlyobtained correspondence of the addresses before and after the currentmigration.

The address conversion post transmission unit 38 detects the networksatisfying the following conditions with referring to the data hold unit1 and then transmits the address conversion post message to thebroadcast address of the detected network. That is, the addressconversion post message is transmitted to the network where the addressassigned before the migration, which is held in the data hold unit 1, isother than 0 as well as the migration communication control deviceemployed as the gateway is not attached. Although in the migration fromthe network 2 to the network 3, the data hold unit 1 holds m at theaddress assigned before the last migration, the gw 2 is attached to thenetwork 1; therefore, the unit 38 does not transmit the addressconversion post to the network 1.

The packet 62 is also received by gw 3. When receiving the packet 62,the gw 3 employs its own devices in FIG. 3 to process the packet 62,which is substantially same as does the gw 2 except the following. Thatis, the address conversion post transmission unit 38 of the gw 3 detectsthat the gw 3 is not attached to the network 1. Also it is detected thatthe mobile host 11, attached to the network 1, has the address m as theaddress assigned before the last migration. Therefore, the unit 38 ofthe gw 3 transmits to the broadcast address of the network 1 a packetcomprising the address conversion post message, which is referred to asa packet 63. FIG. 12(c) shows the packet 63.

The packet 63 is received by the gw 2, the gw 1, both of which areattached to the network 1. Although it is also received by thestationary host 11, this will not be described here. Obtaining thecurrent address correspondence m′-m″ from the packet 63, where m′coincides with the address which has been held in the hold unit 1 at theaddress obtained after the migration, the gw 1 changes the m-m′ in thedata hold unit 1 into the m-m″ by replacing m′ with m″ as the addressassigned after migration.

On the other hand, the data hold unit 1 of the gw 2 had gained from thepacket 62 the above information before receiving the packet 63.Therefore the content of the unit 1 of the gw 2 does not change acrossreception of the packet 63. This is because the gws of the presentinvention locate on a gateway, which connects a couple of networks. Dueto its location, each gw receives packets from two networks. However,actually the-packet 62 is destined for the network 2 and the packet 63is destined for the network 1. Therefore, even though the gw 2, whichare attached to both the network 1 and the network 2, receives both thepacket 62 and 63 by the gw 2, this will not cause any problem in thecommunication between the stationary host 12 and the mobile host 11.

FIG. 13(b) shows the content of the data hold unit 1 in each of the gws.

(Migration from Network 3 to Network 4)

When migrating from the network 3 to the network 4, the mobile host 11obtains m′″ as the address assigned after the migration. Then the mobilehost 11 sends to the gw 3 and a gw 4, both of which are attached to thenetwork 3, a packet comprising the migration post message. The packetreceived by the gw 3 is referred to as a packet 64. The broadcastaddress of the network 3 can be employed as the destination address ofthe packet 64. When the packet 64 is destined for the broadcast addressof the network 3, every host attached to the network 2, which includesthe gw 3 and the gw 4, obtains from the packet the correspondence of theaddresses each of which assigned before and after the migration from thenetwork 3 to the network 4.

The gw 3 employs its devices in FIG. 3 to process the packet 64. Thatis, receiving the packet 64, the gw 3 converts the content of the datahold unit 1 by replacing the address correspondence m-m″ with m-m′″,newly holding m″-m′″ obtained from the packet 64 as well as the addressm′ assigned before the last migration. Then, the address conversion posttransmission unit 38 of the gw 3 transmits the address conversion postmessage to the network satisfying the following condition. That is, theaddress conversion post message is transmitted to the network where theaddress assigned before the migration, which is held in the data holdunit 1, is other than 0 as well as the gw 3 it self is not attached. Thepacket including the address conversion post message is referred to apacket 65, and the packet is transmitted to the broadcast address of thenetwork 1. FIG. 7(c) shows the packet 65.

The packet 64 is also received by gw 4. When receiving the packet 64,the gw 4 renews the content of the data hold unit 1 by replacing m′-m″with m′-m′″ as well as newly holding the address m′ as the addressassigned before the last migration. Further, the address conversion posttransmission unit 38 of the gw 4 detects that the gw 4 is not attachedto the network 2 which has the address other than 0 at the addressassigned before the last migration; therefore, the unit 38 of the gw 4transmits a packet comprising the address conversion post message, whichis referred to as a packet 66, to the broadcast address of the network2. FIG. 7(c) shows the packet 66.

Receiving the packet 65, 65, the gw 2 and the gw 1 renew the content ofits data hold unit 1, which is substantially the same as the above.

The gw 3 and the gw 2 receives the same information twice since theformer receives the packet 64 and 65 while the latter receives thepacket 65 and 66. This is because gws of the present invention locate ona gateway and receives packets from a couple of networks, which isdescribed the above.

FIG. 13(c) shows the content of the data hold unit 1 in each of the gws.Thus, according to the gws of the present invention, the packettransmitted to any of the addresses m, m′, m″ is transferred by the gwsto the updated address of the mobile host, the gws also notify thestationary host of the updated address.

For example, when the stationary host is not notified of the updatedaddress of the mobile host and transmits a packet to the address m′, thepacket is received by the gw 2 and the gw 3, both of which are attachedto the network 2. Then, the gw 2 and the gw 3 transfers the packet tothe updated address of the mobile host as well as notifies thestationary host of the updated address. Thereby, the stationary hostobtains the updated address of the mobile host, so that it will be ableto communicate with the mobile host directly. The packet destined forthe address m′ is received by both the gw 2 and the gw 3, since they areattached to the network 2. Thus, the mobile host receives the samepacket twice, once from the gw 2 and the other time from the gw 3, andthe stationary host receives the same message twice; however, therepeated packet or the message can be simply ignored, so that this willnot cause any problem in the communication between the stationary hostand the mobile host. The repeated packet or the message is observed whenthe two gws are attached to each network in FIGS. 7a-7 c; whereas it isnot observed when only one migration communication control device isattached to each network, which will be described later at the operationin FIGS. 9a-9 c.

(Operation Example in FIG. 8)

In FIG. 6, FIGS. 7a-7 c, the stationary host transmits the data packetto the outdated address after the mobile host notifies the gws that ithas migrated to another network. Then the gws transmit the addressconversion post message to the stationary host. However, in FIG. 8 thegws convert the destination address of the data packet from the outdatedaddress into the updated address assigned after the migration instead oftransmitting the address conversion post message.

A packet 71, 72 in FIG. 8 are substantially same as the packet 51, 52 inFIG. 6. The operation conducted before the packet 72 is transmitted bythe stationary host 12 and is received by the gateway 13 issubstantially same as the first operation in FIG. 6. The operation whichfollows reception of the packet 72 is described hereunder with referringto FIG. 3.

The gate way 13 employs its units in FIG. 3 to process the packet 72.The communication control unit 4 receives the packet 72 and gives it tothe reception packet unit 35 in the migration address unit 3. Detectingthat the packet 72 is a general packet, the reception packet unit 35sends it to the address comparison unit 37. The address comparison unit37 detects whether or not the destination address of the packet 72coincides with the address in the data hold unit 1 at the addressassigned before the migration.

When no coincidence is found, the address comparison unit 37 gives thepacket 72 to the application unit 2. On the other hand, a coincidence isfound, the address assigned after the migration, which corresponds withthe address identical to the destination address of the packet 72, isobtained from the data hold unit 1, and is sent to the marked packetconversion unit 39 together with the packet 72. The marked packetconversion unit 39 generates a packet 72′ where the destination addressof the packet 72 is replaced with the address assigned after themigration, which is sent by the address comparison unit 37, thedestination address of the packet 72 is added as additional address, anda mark is set to indicate that the destination address has converted.Then the packet 72′ is sent to the communication control unit 3. FIG.12e shows a format of the packet 72′, where identical numerals denotethe same units in FIGS. 11a-11 f. The packet 72′ is sent to the mobilehost 11 without fail since its destination address is the updatedaddress thereof.

(Operation Example in FIG. 9)

In FIGS. 9a-9 c, the mobile host migrates across network 1, 2, 3, and 4.In FIGS. 7a-7 c, the gw 1-gw 4 are employed as the migrationcommunication control devices; whereas in FIGS. 9a-9 c, the gw 1-gw 4are employed simply as gateways to connect networks, and also anothermigration communication control device is attached to each network. Theoperation of the migration communication control device, which isconnected to the network alone, at processing the migration post messageor the address conversion post message is substantially the same as oneof the gw 1-gw 4 in FIGS. 7a-7 c. The flow of the migration post messageand the address migration post message are mainly described hereunder.

(Migration from Network 1 to Network 2)

When migrating from the network 1 to the network 2, the mobile host 11sends a packet comprising the migration post message to the migrationcommunication control device, which is attached to the network 1. InFIG. 9(a) a migration post packet 81 is transmitted to a migrationcommunication control device S1, which is attached to the network 1. Thedestination address of the packet 81 can be the broadcast address of thenetwork 1.

The device S1 processes the packet 81 by employing its devices in FIG.3. Receiving the packet 81, the device S1 stores into the data hold unit1 the correspondence of the addresses each assigned before and after themigration as well as the address assigned before the last migration. Themigration post information unit 36 transmits the packet 81 to theaddress conversion post transmission unit 38; however, since the unit 38detects that the address assigned before the last migration is 0, itdoes not transmit the address conversion post message to any network.The content of the data hold unit 1 in the S1-S4 are shown in FIG.14(a).

(Migration from Network 2 to Network 3)

When migrating from the network 2 to the network 3, the mobile host 11notifies the S2, which is attached to the network 2, that it hasmigrated to the network 3 by transmitting thereto the packet comprisingthe migration post message, which is referred to as a packet 82 in FIG.9(b).

The S2 employs its devices in FIG. 3 to process the packet 82. That is,it converts the content of the data hold unit 1 by renewing and addingnew information, and finally holds in the unit 1 the address m′-m″ atthe correspondence of the addresses each of which assigned before andafter the migration as well as the address m assigned before the lastmigration. Then, the migration post information unit 36 gives the newlyobtained correspondence m′-m″ to the address conversion posttransmission unit 38.

The address conversion post transmission unit 38 detects whether or notthe address assigned before the last migration, which is held in thedata hold unit 1, is 0. If the address is not 0, the unit 38 transmitsthe address conversion post message to the broadcast address of thenetwork which includes the detected address. In FIG. 9(b) the address mis held at the address assigned before the last migration, so that theunit 38 transmits the packet 83 to the broadcast address of the network1.

When receiving the packet 83, the migration communication control deviceS1, which is attached to the network 1, renews the content of the datahold unit 1 by newly holding the address correspondence m-m″ as well asthe address 0 at the address assigned before the last migration.Detecting 0 at the address assigned before the last migration, theaddress conversion post transmission unit 38 does not transmit theaddress conversion post to any network. The content of the data holdunit 1 in the S1-S4 are shown in FIG. 14(b).

(Migration from Network 3 to Network 4)

When migrating from the network 3 to the network 4, the mobile host 11notifies the communication migration control device S3, which isattached to the network 3, that it has migrated to the network 4 bytransmitting thereto a packet comprising the migration post message,referred to as a packet 84 in FIG. 9(c).

The migration communication control device S3 employs its devices inFIG. 3 to process the packet 84. That is, it newly holds into the datahold unit 1 the address correspondence m″-m′″ as well as the address m′assigned before the last migration. Then, the address conversion posttransmission unit 38 in the 53 transmits a packet comprising the addressconversion post message, referred to a packet 85 in FIG. 9(c), to thebroadcast address of the network 2 since the address m′ is held at theaddress assigned before the last migration in the data host unit 1.

When receiving the packet 85, the migration communication control deviceS2 employs its devices in FIG. 3 to process it. That is, it newly holdsinto the data hold unit 1 the address correspondence m′-m″ as well asthe address m assigned before the last migration. Then, the addressconversion post transmission unit 38 in the S2 transmits a packetcomprising the address conversion post message, referred to a packet 86in FIG. 9(c), to the broadcast address of the network 2 since theaddress m is held at the address assigned before the last migration inthe data hold unit 1.

When receiving the packet 86, the migration communication control deviceS1 employs its devices in FIG. 3 to process it. That is, it newly holdsinto the data hold unit 1 the address correspondence m-m′″ as well asthe address 0 at the address assigned before the last migration. Theaddress conversion post transmission unit 38 in the S1 does transmit theaddress conversion post since 0 is detected at the address assignedbefore the last migration. The content of the data hold unit 1 in eachof the S1-S4 are shown in FIG. 14(c). Thus, according to the migrationcommunication control device S1-S4 of the present invention, the S1-S4are notified of the updated address of the mobile host at everymigration, so that the packet transmitted to any of the addresses m, m′,m″ is transferred thereby to the updated address of the mobile host. TheS1-S4 also notify the stationary host of the updated address of themobile host.

The operation in FIGS. 9a-9 c differs from the operation in FIGS. 7a-7 cin that each network has just one communication migration control device(one of the S1-S4), so that the migration post and the addressconversion transmitted to S1-S4 are not duplicated.

In the format shown in FIGS. 11a-11 f and 12 a-12 e, the mark 96 or themessage type 93 indicates a kind of packet. That is, mark 96 indicateswhether or not the packet is marked while the message type 93 indicateswhether it is the packet comprising the migration post message, thepacket comprising the address conversion post message, and the generalpacket. Further, a protocol type can also be employed to indicate whichmigration communication control device is employed. For example, whenTCP/IP is employed, the protocol number at the IP header thereofdistinguishes the packet employed in the embodiment from other packets.That is, when the protocol number in the packet is identical with theone, which has been assigned to the protocol number field, the packet isthe one employed in the embodiment.

In the first embodiment of the present invention, a nonvolatile storagecan be employed as the data hold unit 1 of the mobile host. If so, thecommunication can be resumed even after the host or the gateway isturned off as well as after the system is reset.

Also even when the stationary host employs the nonvolatile storage asthe data hold unit 1, it can resume the communication, which hasinterrupted by the switch off or the system reset, rather fast since itobtains from another host the updated address of the mobile host insteadof receiving from the gateway the address conversion post message whichshows the updated address.

For example, it is supposed in FIGS. 7a-7 c that the mobile host 11migrates from the network 1 to the network 4. The data hold unit 1 ofthe migration communication device holds the address correspondencem-m′″ since it has communicated with the mobile host, which is attachedto the network 4, at least once. According to the migrationcommunication control device in the embodiment described above, thepacket is transferred from the outdated address to the updated addressof the mobile host and the stationary host is notified of the updatedaddress; therefore, even when the address information in the data holdunit is lost by switch off thereof, the stationary host will obtain theupdated address. Restart of the communication can also be implemented byemploying a specific host such as a server. That is, the server may beconstructed to obtain the updated address of the mobile host at everymigration, and give it to the stationary host whenever requested. Inthis case a packet comprising the address inquiry should be generatedbeforehand.

Also in the fifth operation in FIG. 6, the mobile host 11 employs theapplication unit 2 and sends to the marked packet conversion unit 21 theaddress assigned before the migration when transmitting the non-responseaddress to the stationary host after it has migrated to another network.Instead of sending the non-response address, the application unit 2 cantransmit a connection identifier to the marked packet conversion unit21. In this case the data hold unit of the migration communicationcontrol device, employed as the mobile host, holds a correspondencebetween the connection identifier and the address that had been assignedwhen the connection was established instead of holding thecorrespondence between the correspondence of the addresses each assignedbefore and after the migration. Then, the unit 21 obtains the sourceaddress of the packet by detecting the address which corresponds to theidentifier, which is held in the data hold unit 1.

As is described the above, the mobile host can employ the broadcastaddress of the network when transmitting the migration post to themigration communication control devices. When the broadcast address isemployed, every host attached to the network, to which the migrationcommunication control device is also attached, obtains the updatedaddress of the mobile host. This implements a direct communicationbetween the mobile host and the stationary host, which improvesefficiency of the communication.

The address assigned before the last migration, which is held in thehold unit 1, can be replaced with the broadcast address assigned to thenetwork to which the mobile host is attached before the last migration.If the broadcast address is employed, the gateway employed as themigration communication control device (gws) or the migrationcommunication control device (Ss) needs to include the broadcast addressin the address conversion post message. In this case both devices canobtain the broadcast address from the data hold unit; therefore, theoperation thereof at requesting the broadcast address will beeliminated.

When storage capacity of the data hold unit 1 is limited, the data holdunit 1 holds only the useful data by disposing the unuseful data, whichis least recently retrieved therefrom by the address comparison unit.

[Embodiment 2]

In FIG. 15 network A, B, and C are connected in a line via gateways 143and 143′, the gateway 143 placing between the network A and B while thegateway 143′ placing between the network B and C.

A home migration communication control device 101 including a migrationaddress unit 144 is attached to the network A; a visitor migrationcommunication control device 109 including a migration address unit 145is attached to the network B; and a visitor migration communicationcontrol device 109′ including a migration address unit 145′ is attachedto the network C. A mobile host 146 including a migration address unit115 is attached to the network A as its home network, and a stationaryhost 151 including a migration address unit 125 is also attached to thenetwork A.

The mobile host 146 migrates across the network A, B, and C. It has ahome address α assigned when it is attached to the network A, as well asother addresses assigned depending on where it migrates, such as atemporary address β on the network B and a temporary address γ on thenetwork C.

Also each of the home migration communication control device 101, thevisitor migration communication control device 109, 109′ which areidentical in its construction and the stationary host 151 has an addressHa, Va, Va′, and Sa respectively assigned on the network.

Detailed function of the above devices 101, 109, 109′, 146, and 151 isdescribed hereunder, in which like components are labeled with likereference numerals.

[Home Migration Communication Control Device 101]

When the mobile host 146 migrates from the home network to anothernetwork, it is assigned the temporary address. However if the stationaryhost 151 is not notified of that migration, it transmits an originaldata packet (hereinafter referred to as a noncapsulated data packet) tothe home address α of the mobile host 146. When the noncapsulated datapacket is destined for the outdated address of the home mobile host 146,the home migration communication control device 101 transfers thatnoncapsulated data packet from there to the updated address, that is thetemporary address β or γ of the mobile host. Then, the device 101 poststo the stationary host 151 the temporary address β or γ here, so thatthe stationary host 151 will be able to communicate directly with themobile host. The device 101 also posts the same information to thevisitor migration communication control device 109, 109′, so that thedevices 109, 109′ will implement the same function with the homemigration communication control device 101.

As shown in FIG. 16 the home migration communication control device 101consists of the migration address unit 144 and a communication controlunit 108. The migration address unit 144 further comprises a home mobilehost (MH) list hold unit 102, a packet transfer unit 103, a mobile host(MH) transfer unit 104, an address inquiry unit 105, a packet monitoringunit 106, an address post unit 107.

Next the function of each component integrating the device 101 will bedescribed. The communication control unit 108 mainly controls thecommunication of protocols located in lower layers including a physicallayer, such as the protocol lower than IP.

The address post unit 107 receives from the mobile host 146 on a datapacket including an address post message. The address post message isgenerated when the mobile host 146 migrates to the network B or C, andposts the temporary address β or γ of the mobile host to the device 101.The unit 107 sends the address post message to the mobile host transferunit 104 as well as sends a response message to the mobile host 146.FIG. 28C is an example of the address post message, which includes thehome address α as well as the temporary address β or γ of the mobilehost 146, a value of an autonomous flag F, and a broadcast address Bba,Cba on the network B, C. The autonomous flag F will be described later.FIG. 28D is an example of the response message.

A mobile host transfer unit 104 stores the address post message into thehome mobile host list hold unit 102, notifies the visitor migrationcommunication control device 109 or 109′ of the migration of the mobilehost 146 by sending thereto a mobile host transfer message, and receivesthe data packet including the response. Further, according to adirection given by the packet transfer unit 103, the unit 104 transmitsthe mobile host transfer message both to the stationary host 151 and thedevice 109 or 109′. The unit 103 gives the direction when the value ofthe autonomous flag F is 1.

FIG. 32C and FIG. 36E are examples of the mobile host transfer messageincluding the home address α, the temporary address β or γ, and theautonomous flag F. Since the mobile host transfer message is sent to thestationary host 151, it is sent only when the autonomous flag F is 1;therefore, it does not necessarily include the value of the flag F.However, the identical message is sent both to the stationary host 151and the visitor migration communication control device 109, 109′ in thisembodiment to simplify the construction of the mobile host transfer unit104. FIG. 32D is an example of the response message.

As shown in FIG. 17, the home mobile host list hold unit 102 holds thehome address α, the temporary address β, γ, the value of the autonomousflag F, and the broadcast address Bba, Cba on the network B, C, all ofwhich are obtained from the mobile host transfer unit 104.

The packet monitoring unit 106 receives the packet destined for the homeaddress α of the mobile host 146, then sends it to the packet transferunit 103 when the stationary host 151 transmits the packet to the homeaddress α of the mobile host 146 after the mobile host 146 has migratedto another network.

The packet transfer unit 103 has a payload including the noncapsulateddata packet and the packet transfer message informing the transfer ofthe noncapsulated data packet, generates another data packet, and sendsit to the temporary address β, γ of the mobile host 146. FIG. 32B is anexample of the packet transfer message. As is described above, thepacket transfer unit 103 directs the mobile host transfer unit 104 totransmit the mobile host transfer message to the stationary host 151only when the autonomous flag in the home mobile host list hold unit 102shows the value of 1. The operation conducted when the flag F is 1 willbe described later.

When the stationary host 151 has problems in communicating with themobile host 146 such as receiving the unusual mobile host transfermessage, the address inquiry unit 105 is employed to solve the problems.That is, receiving from the stationary host 151 an address inquirymessage, the address inquiry unit 105 transmits to the stationary host151 a data packet which responds to the address inquiry by showing theaddress to be used in the communication. The address inquiry messageincludes a type field 132, a flag field 133, a sequence field 134, and ahome address field 138, each of which having value 5, 1, a certainnumber, and α respectively; while the response message includes atemporary address field 139 filled with the temporary address β, γ aswell as the flag field with 2, besides the type field 132, the sequencefield 134, and the home address field 138 filled with the same values inthe address inquiry message.

[Visitor Migration Communication Control Device 109]

The visitor migration communication control device 109 implements thesame function with the home migration communication control device 101.That is, when the stationary host 151 transmits an encapsulated datapacket to the temporary address β of the mobile host 146, which is theupdated address thereof since the mobile host has migrated to thenetwork C, the visitor migration communication control device 109transfers that encapsulated data packet from the temporary address β totemporary address γ. Then, the device 109 posts to the stationary host151 the temporary address γ, so that the stationary host 151 will beable to communicate directly with the mobile host 146. However, whetheror not the device 109 provides the above packet transfer service will bedetermined in accordance with a processing load put on the device 109 orwith a initial setting given by a system operator; thus, the packettransfer service of the device 109 is not necessarily an obligation.

As shown in FIG. 18, the visitor migration communication control device109 consists of the migration address unit 145 and the communicationcontrol unit 108. The migration address unit 145 further comprises thepacket monitoring unit 106, a visitor mobile host list hold unit 110, apacket transfer unit 111, a mobile host transfer unit 112, a mobile hostvisit unit 113, and an autonomous support unit 114. The unit 106 and theunit 108 function the same as those in the home migration communicationcontrol device 101.

Receiving an autonomous packet transfer support check message inquiringif the visitor migration communication control device 109 provides thepacket transfer service, the autonomous support unit 114 responds to itwith the response message where the autonomous flag F shows 1 when thedevice 109 provides that service or 0 when it does not provide thatservice. FIG. 28A is an example of the autonomous packet transfersupport check message, while FIG. 28B is an example of the responsemessage including the autonomous flag F and the broadcast address Bba.

Receiving from the mobile host 146 the mobile host visit message whichinforms that the mobile host 146 has migrated to the network B, themobile host unit 113 responds it with the response message after storingthe mobile host visit message into the visitor mobile host list holdunit 110. The mobile host visit message includes the home address α andthe temporary address β of the mobile host 146. FIG. 28E is the formatof the mobile host visit message, while FIG. 28F is the format of theresponse message.

Receiving from the mobile host transfer unit 104 in the device 101 themobile transfer message informing that the mobile host 146 has migratedto the network C, the mobile host transfer unit 112 stores in thevisitor mobile host list hold unit 110 the updated temporary address γof the mobile host 146 and the value of the autonomous flag F bycorresponding them to the home address α. The unit 112 also transmits tothe stationary host 151 the mobile host transfer message in accordancewith the direction from the packet transfer unit 111, as does the mobilehost transfer unit 104 in the device 101.

As shown in FIG. 19, the visitor mobile host list hold unit 110 holdsthe home address α and the temporary address β on the network B, whichare obtained from the mobile host 146 via the mobile host visit unit113, as well as the temporary address γ and value on the autonomous flagF, which are obtained from the home migration communication controldevice 101 via the mobile host transfer unit 112.

The packet transfer unit 111, as does the packet transfer unit 103 inthe home migration communication control device 101, transmits to thetemporary address γ the data packet including the transfer message aswell as orders the mobile host transfer unit 112 to transmit the mobilehost transfer message.

[Mobile Host 146]

As shown in FIG. 20, the mobile host 146 includes the migration addressunit 115, an address obtainment unit 116, the communication control unit108, and an application processing unit 124 which mainly controls thecommunication of protocols located in higher layers including anapplication layer, such as TCP or layers located higher than it.

The migration address unit 115 comprises the a packet transmission unit117, a transfer packet reception unit 118, an address hold unit 119, amigration unit 120, an autonomous support unit 121, an address post unit122, a mobile host visit unit 123.

The migration address unit 115 comprising the above units is employed intransfer of data to the temporary address β or γ when the mobile host146 migrates to the network B or C. Also receiving the data packetdestined for the temporary address β or γ including the packet transfermessage and the noncapsulated data packet, the device 115 transmits thenoncapsulated data to the application processing unit 124.

In accordance with the order given by the application processing unit124 when the mobile host migrates to the network B, C, the migrationunit 120 controls the address obtainment unit 116, the autonomoussupport unit 121, the address post unit 122, the mobile host visit unit123, and the address hold unit 119.

Directed by the migration processing unit 120, the address obtainmentunit 116 obtains the temporary address β, γ of the mobile host 146assigned when it migrates to the network B, C respectively. BOOTP in“Bill Croft and John Gilmore, BOOTSTRAP PROTOCOL RFC951, Sep., 1985” isan example of obtaining the temporary address; besides employing theBOOTP, the operator may input the temporary address β, γ assigned by asystem administrator of the network B, C.

Directed by the migration unit 120, the autonomous support unit 121sends the autonomous packet transfer support check message to inquire ifthe visitor migration communication control device 109, 109′ attached tothe network B, C provides the packet transfer service and receives theresponse message to the inquiry. The autonomous packet transfer supportcheck message is also sent to obtain the broadcast address Bba and Cbaon the network B and C respectively.

Directed by the migration unit 120, the address post unit 122 sends theaddress post message to notify the home migration communication controldevice 101 of the temporary address β, γ. The address post message alsoinforms whether or not the device 109, 109′ provides the packet transferservice as well as the broadcast address Bba, Cba on the network B, C.If the response message from the visitor migration communication controldevice 109, 109′ has the value 1 of the autonomous flag F, the mobilehost visit unit 123 transmits to the visitor migration communicationcontrol device 109, 109′ the mobile host visit message including thehome address α as well as the temporary address β, γ respectively.

As shown in FIG. 21, the address hold unit 119 previously holds the homeaddress α of the mobile host 146 and the broadcast address Aba on thenetwork A. Now, the unit 119 newly holds the temporary address β or γobtained from the address obtainment unit 116 via the migration unit 120and the broadcast address Bba or Cba obtained from the autonomoussupport unit 121 via the migration unit 120.

When the mobile host 146 is attached to the network A and receiving adata packet destined for the home address α, the transfer packetreception unit 118 sends data etc. in the noncapsulated data packet tothe application processing unit 124. On the other hand, when the mobilehost 146 is attached to the network B and receiving a data packetdestined for the temporary address β, the data packet including thepacket transfer message and the noncapsulated data packet destined forα, the unit 118 sends to the application processing unit 124 data etc.in the noncapsulated data. Thus, the application processing unit 124receives the data without being affected by the migration of the mobileacross the networks.

Receiving the data to be transmitted and the instruction from theapplication processing unit 124, the packet transmission unit 117generates a noncapsulated data packet whose destination address is thehome address α and transmits it.

[Stationary Host 151]

As shown in FIG. 22, the stationary host 151 comprises the migrationaddress unit 125 and the application processing unit 161 which mainlycontrols the communication of a protocol located in higher layersincluding application layer, such as TCP or layers located higher thanthe TCP and the communication control unit 108.

The migration address unit 125 comprises a transfer packet transmissionunit 126, a packet reception unit 127, an address hold unit 128, anaddress inquiry unit 129, and the mobile host transfer unit 130.

The migration address unit 125 comprising the above units generates anoncapsulated data packet and sends it to the home address α when it isnot notified that the mobile host 146 migrate to the network B or C andobtained the temporary address β or γ respectively. The unit 125 alsogenerates an encapsulated data packet including as a payload thenoncapsulated data packet and a data transfer message, which informstransfer of the noncapsulated data packet and sends it to the temporaryaddress β, γ, when it is notified of the migration.

Receiving from the home migration communication control device 101 andthe visitor migration communication control device 109, 109′ the datapacket including the mobile host transfer message which informs themigration of the mobile host 146, the mobile host transfer unit 130stores into the address hold unit 128 the home address α and thetemporary address β or γ of the mobile host 146 assigned on the networkB or C respectively.

As shown in FIG. 23, the address hold unit 128 holds the home address α,the temporary address β or γ by corresponding them.

Directed by the application unit 161, the transfer packet transmissionunit 126 generates a data packet destined for the home address α, andtransmits it. However, if the address hold unit 128 holds the temporaryaddress β or γ besides the home address α, the unit 126 generates anencapsulated data packet destined for the temporary address β or γ,which includes as a payload a noncapsulated data packet and a packettransfer message, which informs transfer of the noncapsulated datapacket, and transmits it.

As is described the above, both the home migration communication controldevice 101 and the visitor migration communication control device 109,109′ generate the encapsulated data packet including the packet transfermessage and the noncapsulated data and transmits it to the currenttemporary address of the mobile host 146. Owing to the device 101 or109, 109′, the stationary host 151 is able to transmit to the mobilehost 146 both the noncapsulated data packet destined for the homeaddress α and the encapsulated data packet destined for the temporaryaddress β or γ without failure even when the address hold unit 128 failsto hold the current temporary address β or γ and the stationary host 151transmits the data packet to the outdated address of the mobile host146.

The packet reception unit 127 receives a data packet which is sent fromthe mobile host 146 and has Sa as its destination address, and sends thedata etc. in it to the application unit 161.

When the address inquiry unit 129 has problems such as that it receivedan illegal mobile host transfer message or that it cannot communicatewith the mobile host 146 successfully, it transmits a data packetincluding an address inquiry message in order to inquire of the hostmigration communication control device 101 the address which iscurrently used to communicate with the mobile host 146.

[Construction of Data Packet]

As shown in FIGS. 24(a), (b), (c), there are three kinds of datapackets, each data packet 210, 220, 230, includes each of header 211,221, 231 and payload 212, 222, 232 respectively.

The header 211 of the data packet 210 includes a destination address201, and a source address 202. Also the payload 212 consists of atransmission data 203.

The header 221 of the data packet 220 includes the destination address201 and the source address 202. Also the payload 222 consists of amessage 204.

The header 231 of the data packet 230 includes the destination address201 and the source address 202. Also the payload 232 consists of themessage 204, which is employed as the packet transfer message, and anoncapsulated data packet 210. Also each header 211, 221, 231 includesinformation showing presence or absence of the message 204 as a protocolnumber etc.

The message 204 includes some of the fields in FIG. 25 in accordancewith its type.

The type of the message 204 is indicated in the message type field 132.Besides the above types, the message 204 is also employed as an echomessage for examining whether or not a host employs an appropriateoperation in accordance with the message.

A flag field 133 indicates whether or not the message 204 is a response.When the message 204 is not the response, the field 133 furtherindicates whether or not the message 204 requests a response.

A sequence field 134 gives a single number both to the request messageand its response message, thereby the request message and the responsemessage are corresponded.

An autonomous flag field 135 contains a value of the autonomous flag Findicating whether or not the visitor migration communication controldevice 109,109′ provide the packet transfer service.

A counter field 136 contains a counter indicating the number of thevisitor migration communication control devices employed to transfer theencapsulated data packet consisting of the packet transfer message andthe noncapsulated data packet. The visitor migration communicationcontrol device increments the counter in the received message packet by1, and gives it to the message to be transmitted. When the incrementednumber is greater than the predetermined number, the received messagepacket is disposed.

A status field 137 of the response message indicates presence or absenceof an error in a transmission/reception of the data packet. For example,it indicates an error in authentication information, which will bedescribed later, or the address inquiry message which cannot or shouldnot be responded.

A home address field 138, a temporary address field 139, and a broadcastaddress field 140 indicates the home address as well as the temporaryaddress of the mobile host 146 or the broadcast address on its homenetwork or on the network it migrates. However, what the broadcastaddress field 140 indicates depends on type of the message 204. Whetherthe message 204 is the request or the response also devices the contentof the broadcast address field 140.

The authentication information field 141 indicates if a source addresscoincides with the sender's address.

[Outline of Communication Operation]

The home migration communication control device 101 and the visitormigration communication control device 109,109′ is basically employed totransfer the data packet transmitted by the stationary host 151 as wellas post to the stationary host 151 the updated temporary address of themobile host 146. Understanding of such operations will be helped by thefollowing two points.

1. Transfer of the data packet and posting of the updated temporaryaddress are conducted only when the mobile host 146 migrates from itshome network to another network. The home network refers to the one towhich the home migration communication control device is attached.

2. Posting of the updated temporary address is conducted only when theautonomous flag F is 1, which indicates the visitor migrationcommunication control device 109, attached to the same network as is themobile host 146, provides the packet transfer service. Otherwise, thedata packet transmitted by the stationary host 151 to the postedtemporary address will not be received by the mobile host 146 when themobile host 146 migrates to another network.

[Communication Operation 1]

An example of the communication operation is described hereunder. In thecommunication operation 1 the visitor migration communication controldevice 109,109′ provides the packet transfer service when the mobilehost 146 migrates from the network A to the network B, further from thenetwork B to the network C.

[Migration from Network A to Network B]

The operation at the migration of the mobile host 146 from the network Ato the network B is described with referring to FIGS. 26-29. FIG. 26shows a flow of the data packet transmitted between the devices; FIG. 27shows a communication sequence of the data packet; FIGS. 28A-28F showconstruction of each data packet; and FIG. 29 shows the content of theaddress hold unit 119 etc.

When the mobile host 146 is attached to the network A, the home mobilehost list hold unit 102 in the home migration communication controldevice 101 holds the home address α both as the home address and thetemporary address of the mobile host 146. Thereby the home migrationcommunication control device 101 detects that the mobile host 146 isattached to the network A.

The address hold unit 119 in the mobile host 146 holds the home addressα and the broadcast address Aba on the network A.

When the mobile host 146 migrates to the network B, the application unit124 orders the operation of the migration unit 120 in accordance withthe instruction given by the operator. The temporary address β isassigned to the mobile host 146 on the network B, and the addressobtainment unit 116 obtains it. The migration unit 120 stores into theaddress hold unit 119 the temporary address β together with the homeaddress α and the broadcast address Aba.

(1) The autonomous support unit 121 transmits to the visitor migrationcommunication control device 109, which is attached to the network B.the data packet including the autonomous packet transfer support checkmessage 147 which holds the home address α and the temporary address β.The destination address of the data packet is the broadcast addressshared by every network, such as an address where every bit is 1. Themessage 147 does not necessarily hold the home address α and thetemporary address β although they can be used in checking the securityof the network if it does. Also the message 147 holding the home addressα and the temporary address γ can take the place of a mobile host visitmessage 146, which will be described later.

(2) The autonomous support unit 114 in the visitor migrationcommunication control device 109 responds to the autonomous support unit121 with the response message 147R where broadcast address Bba is setand the autonomous flag F in the autonomous flag field 135 indicates 1to inform that the device 109 provides the packet transfer service.

The mobile host 146 transmits the data packet to the visitor migrationcommunication control device 109. The broadcast address Bba is employedas the destination address of the data packet and it is set in theresponse message 147R; however, this is not an obligation.

That is, when the response message 147R does not hold the broadcastaddress Bba, the following means can be employed. First, the broadcastaddress shared by every network can be employed, which is described inthe above. Second, the source address, which is set in the header of thedata packet comprising the response message 147R, can be employed.Third, a so called name service can be employed, where a server deviceon the network system informs the broadcast address Bba. Finally, whenthe address assigned to each of the devices, which are attached to thenetwork, consists of the network address being unique for the networkand a device address being unique for the devices, and the broadcastaddress on each network consists of such network address and the deviceaddress where the value of every bit is 1, the network address Bba canbe generated by employing the network address included in the temporaryaddress β of the mobile host 146.

(3) The address post unit 122 transmits to the home migrationcommunication control device 101 the address post message 148. Themessage 148 includes the value 1 of the autonomous flag F, which isobtained from the response message, home address α, the temporaryaddress β on the network B, and the broadcast address Bba, and thebroadcast address Aba is the destination address of the address postmessage 148.

When the address post unit 107 in the home migration communicationcontrol device 101 receives the address post message 148, the mobilehost transfer unit 104 stores in the home mobile host list hold unit 102the temporary address β, the value 1 of the autonomous flag 1, and thebroadcast address Bba by corresponding them to the home address α. Sincethe home address α had been stored as the temporary address before thetemporary address β was stored, the mobile host transfer unit 104 knowsthat the mobile host 146 has migrated from the network A to the networkB; therefore, it does not transmit the mobile host transfer message tothe visitor migration communication control device 109,109′. That is,the data packet transmitted by the stationary host 151 to the homeaddress α of the mobile host 146 is received by the home migrationcommunication control device 101 and transferred thereby to thetemporary address β; therefore, the visitor migration communicationcontrol device 109,109′ is not employed here.

(4) The address post unit 107 notifies the address post unit 122 that ithas received the address post message 148 by sending the responsemessage 148R.

(5) Since the visitor migration communication control device 109provides the packet transfer service, the mobile host visit unit 123transmits to the visitor migration communication control device 109 themobile host visit message 149 including the home address α and thetemporary address β, so that the device 109 is notified that the mobilehost 146 has migrated to the network B. The mobile host visit message149 is destined for the broadcast address Bba.

The mobile host visit unit 113 in the visitor migration communicationcontrol device 109 receives the mobile host visit message 149 and storesinto the visitor mobile host list hold unit 110 the home address α aswell as the temporary address β. The temporary address β is stored alsoas the updated temporary address of the mobile host 146, which will beassigned when the mobile host 146 migrates from the network B to anothernetwork; thereby, the visitor migration communication control device 109detects that the mobile host is currently attached to the network B.

(6) The mobile host visit unit 113 notifies the mobile host visit unit123 by sending the response message 149R that it has received the mobilehost visit message 149.

[Communication Between the Stationary Host 151 and the Mobile Host 146on the Network B]

The operation at the communication between the stationary host 151 andthe mobile host 146 when the mobile host is attached to the network B isdescribed hereunder with referring to FIGS. 30-33, which are relevantfor FIGS. 26-29.

(1) The application unit 161 in the stationary host 151 directs thetransmission of the noncapsulated data packet, whose destination is thehome address α, despite the migration of the mobile host 146.Immediately after the mobile host 146 migrates to the network B, thatis, when the address hold unit 128 does not hold the home address α andthe temporary address β, the transfer packet transmission unit 126 isnot notified of the migration; therefore, it generates the noncapsulateddata packet 152 and transmits it to the home address α in accordancewith the direction from the application unit 151.

The noncapsulated data packet 152 is not received by the mobile host146, which is not attached to the network A, but by the packetmonitoring unit 106 in the home migration communication control device101 since the home mobile host list hold unit 102 in the device 101holds the home address α as well as the temporary address β, whichcoincides with the destination address of the noncapsulated data packet152.

(2) The packet transfer unit 103 in the home migration communicationcontrol device 101 generates an encapsulated data packet including thenoncapsulated data packet 152, which is received by the packetmonitoring unit 106, and the packet transfer message 153, which informsthe transfer of the noncapsulated data packet 152; and transmits it tothe temporary address β. The packet transfer message 153 includes thevalue 0 in the field 133, which indicates that no response is requested,as well as the value 0 on the counter in the field 136, which indicatesthat the packet transfer message is the first message added to thenoncapsulated data packet 152. As is described, no response is requestedby the packet transfer message 153. That is, the application unit 161 ofthe stationary host 151 and the application unit of the mobile host 146,rather than the home migration communication control device 101 and themigration address unit 115, confirm that the mobile host 146 receivesthe noncapsulated data packet 152.

The transfer packet reception unit 118 in the mobile host 146 receivesthe encapsulated data packet including the packet transfer message 153and the noncapsulated data packet 152, since it is destined for thetemporary address β, which is held in the address hold unit 119. Theunit 118 then detects that the destination address of the noncapsulateddata packet 152 is the home address α, and sends the data etc. in thenoncapsulated data packet 152 to the application unit 124.

Thus, the communication between the application unit 124 and theapplication unit 161 is not affected by the migration of the mobile host146.

(3) The packet transfer unit 103 transmits the encapsulated data packetincluding the data packet transfer message. It also directs, afterdetecting that the autonomous flag F indicates 1, the mobile hosttransfer unit 104 to transmit to the stationary host 151 the data packetincluding the mobile host transfer message 154 where the home address αand the temporary address β are set. Finally, the unit 104 transmits thedata packet to the stationary host 151.

The mobile host transfer unit 130 in the stationary host 151 receivesthe mobile host transfer message and stores into the address hold unit128 the home address α and the temporary address β.

(4) The mobile host transfer unit 130 responds to the mobile hosttransfer unit 104 with the response message 154R.

(5) When the application unit 161 directs the transmission of thenoncapsulated data packet to the home address α after the address holdunit 128 holds the home address α and the temporary address β, thetransfer packet transmission unit 126 first generates a noncapsulateddata packet destined for the home address α, then generates anencapsulated data packet including it and a packet transfer message 155.The encapsulated data packet is then transmitted to the temporaryaddress β. Thus, once the home migration communication control device101 notifies the stationary host 151 of the home address α and thetemporary address β, the stationary host 151 is able to transmit thedata packet to the temporary address β of the mobile host 146, and thehome migration communication control device 101 is not employed.

On the other hand, when data is transmitted from the mobile host 146 tothe stationary host 151, the Sa is employed as the destination address αand the home address is employed as the source address; and thenoncapsulated data packet is transmitted from the address α to theaddress Sa.

Thus, even when all the noncapsulated data transmitted by the stationaryhost 151 is destined for the home address α, the home migrationcommunication device 101 transfers the data to the updated temporaryaddress of the mobile host; thereby, the communication between themobile host 146 and the stationary host 151 is implemented, and theconventional device can be employed as the stationary host 151, whichbroadens a practicability of the network system.

Whereas, when the network system checks the original source address ofthe data packet or a transfer path of the data packet, the transmissionunit may be built in the mobile host 146 like the transfer packettransmission unit 126 in the stationary host 151, and also the receptionunit may be built in the stationary host 151 like the transfer packetreception unit 118 in the mobile host 146; and the encapsulated datapacket including the packet transfer message and the noncapsulated datapacket may be transmitted therebetween.

[Migration from Network B to Network C]

The operation at the migration of the mobile host 146 from the network Bto the network C is described hereunder with referring to FIGS. 34-37,relevant for FIGS. 26-29.

(1)-(4) The operation related to transmission of an autonomous packettransfer support check message 147′, a response message 147R′, anaddress post message 148′, and a response message 148′ between themobile host 146 and the visitor migration communication control device109′ is substantially same as the operation related to transmission ofmessages between the mobile host 146 and the visitor migrationcommunication control device 109, which is conducted when the mobilehost 146 migrates to the network B. However, the operation at themigration from the network A to the network B and the operation at themigration from the network B and the network C are different from eachother in part of the operation of the home migration communicationcontrol device 101 conducted after it responds to the received addresspost message 148′ with the response message 148R.

(5) When the address post unit 107 receives the address post message148′, the mobile host transfer unit 104 in the home migrationcommunication control device 101 detects that the mobile host beenattached to the network B before migrating to the network C since thetemporary address β has been stored as the temporary address. Then, themobile host transfer unit 104 sends to the visitor migrationcommunication control device 109 the data packet including both the homeaddress α and the temporary address γ, so that the device 109 transfersthe data packet transmitted by the stationary host 151 from thetemporary address β to the temporary address γ. The data packet receivedby the visitor migration communication control device is destined forthe broadcast address Bba.

In accordance with the address post message 148′, the mobile hosttransfer unit 104 stores into the home move host list hold unit 102 thetemporary address γ, the value 1 of the autonomous flag F, and thebroadcast address Cba by corresponding them to the home address α.

Receiving the data packet including the mobile host transfer message150, the mobile host transfer unit 112 in the visitor migrationcommunication control device 109 stores into the visitor mobile hostlist hold unit 110 the temporary address γ newly assigned to the mobilehost 146 and the value 1 of the autonomous flag F by corresponding themto the home address α.

(6) The mobile host transfer unit 112 notifies the mobile host transferunit 104 that it has received the mobile host transfer message 150 bysending thereto the response message 150R.

(7), (8) The transmission of a mobile host visit message 149′ and aresponse message 149R′ between the mobile host 146 and the visitormigration communication control device 109′, which is conducted when thedevice 109′ provides the packet transfer service, is substantially sameas the transmission of messages between the mobile host 146 and thevisitor migration communication control device 109, which is conductedwhen the mobile host 146 migrates to the network B.

[Communication Between Mobile Host 146 Attached to Network C andStationary Host 151]

Transmission of the data packet from the stationary host 151 to themobile host 146 when the mobile host is attached to the network C isdescribed with referring to FIGS. 38-41, which are relevant for FIGS.26-29.

The transmission is substantially same as the transmission between thestationary host 151 and the mobile host 146 when the mobile host 146 isattached to the network B, except that the visitor migrationcommunication control device 109 instead of the home migrationcommunication control device 101 is employed.

(1) When the stationary host 151 is not notified that the mobile host146 has migrated from the network B to the network C, the stationaryhost 151 generates the encapsulated data packet including thenoncapsulated data packet, which is destined for the home address α, andthe packet transfer message 156; then transmits it to the temporaryaddress β. This is substantially the same as (5) in the communicationbetween the stationary host 151 and the mobile host 146 attached thenetwork B.

The data packet transmitted by the stationary host is not received bythe mobile host 146 since the mobile host is not attached to the networkB. The data packet is received by the packet monitoring unit 106 in thevisitor migration communication control device 109 since the visitormobile host list hold list unit thereof holds the temporary address βbesides the temporary address γ.

(2) The visitor migration communication control device 109 transmits tothe temporary address γ of the mobile host 146 the data packet includingthe packet transfer message 157, which is substantially same as (2) inthe communication between the stationary host 151 and the mobile host146 on the network B except a difference described hereunder.

The home mobile host migration communication control device 101 receivesthe noncapsulated data packet 152 and generates an encapsulated datapacket comprising the received noncapsulated data packet 152 and thepacket transfer message 153. On the other hand, the visitor migrationcommunication control device 109 receives the encapsulated data packetcomprising the packet transfer message 156 and the packet transfer unit111 converts the data packet by changing the destination address fromthe temporary address β into the temporary address γ as well asconverting the packet transfer message 156 into the packet transfermessage 157, whose value on the counter is incremented by 1.

(3)-(5) The visitor migration communication control device 109, thestationary host 151, and the mobile host 146 on the network C operatesubstantially same as the home migration communication control device101, the stationary host 151, and the mobile host 146 on the network B,which is described the above in (3)-(5); thereby the mobile hosttransfer message 158 and the response message 158R are transmitted, andthe data packet including the packet transfer message 160 is transmittedby the stationary host 151 to the mobile host 146 attached to thenetwork C.

If the stationary host 151 does not transmit any data packet to themobile host 146, which is attached to the network B, the stationary hostis not notified of either the temporary address β or the temporaryaddress γ; therefore, the stationary host 151 transmits the data packetto the home address α even when the mobile host 146 has migrated fromthe network B to the network C. When this occurs, the home migrationcommunication control device 101, as does the visitor migrationcommunication device 109, transfers the data packet from the homeaddress α to the temporary address γ; then notifies the stationary host151 of the updated temporary address γ of the mobile host 146 so thatthe stationary host 151 will be able to directly transmit the datapacket, which comprises the packet transfer message, to the mobile host146 attached to the network C.

Further, when the mobile host 146 migrates to the network, to which thevisitor migration communication control device is attached to providethe packet transfer service, the stationary host 151 may transmit thedata packet destined for any of the addresses α, β, or γ. When the datapacket is transmitted to the home address α or the temporary address γ,the home migration communication control device 101 or the visitormigration communication control device 109′, which is notified of theupdated temporary address of the mobile host 146, transfers the datapacket to the updated temporary address; then it notifies the stationaryhost 151 of the updated temporary address of the mobile host.

When the data packet is transmitted to the temporary address β of themobile host 146, the visitor migration communication control device 109receives it. Since the device 109 is notified of only the temporaryaddress γ, it transmits the data packet comprising the packet transfermessage to the temporary address γ as well as transmits the mobile hosttransfer message to notify the stationary host 151 of the temporaryaddress γ. The visitor migration communication control device 109′receives the data packet comprising the packet transfer message, whichis destined for the temporary address γ, and transmits it to the updatedtemporary address of the mobile host 146; then transmits the mobile hosttransfer message to notify the stationary host 151 of the updatedtemporary address. Also the visitor migration communication controldevice 109′ obtains the address of the visitor migration communicationcontrol device 109 from. the source address of data packet transmittedthereby, and transmits the mobile host transfer message to the device109. Thus, the visitor migration communication control device 109′obtains the updated temporary address of the mobile host 146, andtransfers the data packet to the mobile host 146 as well as notifiesstationary host 151 of the obtained updated temporary address.

[Communication Operation 2]

Another example of the communication operation is described hereunder.In the communication operation 2 the visitor migration communicationcontrol device 109 does not provide the packet transfer service when themobile host 146 migrates from the network A to the network B, furtherfrom the network B to the network C.

As shown in FIG. 42, when the device 109 does not provide the packettransfer service, the autonomous packet transfer support check message181, transmitted by the mobile host 146 which has migrated from thenetwork A to the network B, is responded with the response message 181Rwhere the autonomous flag F in the autonomous flag field 135 indicates0. Thereby, the autonomous flag field 135 in the address post message182, which is transmitted by the mobile host 146 to the home migrationcommunication control device 101, obtains the value 0, and the value 0is held in the home mobile host list hold unit 102 in the device 101.The mobile host 146 does not transmit the mobile host visit message tothe visitor migration communication control device 109.

As shown in FIG. 43, receiving from the stationary host 151 thenoncapsulated data packet 183, which is destined for the home address α,the home migration communication control device generates theencapsulated data packet comprising the received noncapsulated datapacket 183 and the packet transfer message 184, and transmits it to thetemporary address i, as is in the communication operation 1.

However, recognizing the value 0 on the autonomous flag F, which is heldin the home mobile host list hold unit 102, the device 101 does nottransmit to the stationary host 151 the mobile host transfer messageincluding the temporary address β. Therefore, every data packettransmitted by the stationary host 151 is destined for the home addressα, and it is transferred to the mobile host 146 by the home migrationcommunication control device 101. Thus, the stationary host 151 is notnotified of the temporary address β since the data packet transmitted tothe address other than the home address αis not transferred by thedevice 109; therefore it is not received by the mobile host 146 when itdeparts the network B to migrate to the network C.

When the visitor migration communication control device 109′, which isattached to the network, provides the packet transfer service, the homemigration communication control device 101 notifies the stationary host151 of the temporary address γ when it transmits the noncapsulated datato the home address α, so that the stationary host 151 is able todirectly transmit the data packet comprising the noncapsulated datapacket and the packet transfer message to the mobile host 146 on thenetwork C.

When the visitor migration communication control device 109 does notprovide the packet transfer service, the home migration communicationcontrol device 101 does not necessarily notify the device 109 of thetemporary address γ of the mobile host 146 assigned when it has migratedfrom the network B to the network C. However, the construction of thedevice 101 will be simplified if it conducts the same operation eitheror not the packet transfer service is provided since the visitormigration communication control device 109 ignores the mobile hosttransfer message.

Also the device 109 may respond to the autonomous packet transfersupport check message 181 only when it provides the data packet transferservice; therefore, the presence or absence of the response message 181Rindicates to the mobile host 146 whether or not the data packet transferservice is provided. In the above operation the value 0 of theautonomous F also indicates that the packet transfer service is notprovided, whereas absence of the response message to the message 181 canindicate the absence of the packet transfer service, which will simplifyconstruction of mobile host 146.

[Communication Operation 3]

The final example of the communication operation is described hereunder.In the communication operation 3 the visitor migration communicationcontrol device 109′ does not provide the packet transfer service whilethe visitor migration communication control device 109 does.

As shown in FIG. 44, when the packet transfer service is not provided bythe visitor migration communication control device 109′, the mobile host146 transmits to the home migration communication control device 101 theaddress post message 182′ where the value 0 is set at the autonomousflag F. Then, the home migration communication control device 101transmits to the device 109 the mobile host transfer message 185 bysetting the value 0 at the autonomous flag F.

When detecting the value 0 at the autonomous flag F, the visitormigration communication control device 109 ceases to provide the packettransfer service.

As shown in FIG. 45, even after cease of the data packet transferservice, the stationary host 151 may transmit to the temporary addressthe data packet comprising the noncapsulated data packet and the packettransfer message 186.

When this happens, the visitor migration communication control device109 obtains the noncapsulated data packet 187 from the receivedencapsulated data packet and transmits it to its destination address,the home address α. The noncapsulated data packet 187 is then receivedby the home migration communication control device 101, which isattached to the network A. Finally, the home migration communicationcontrol device 101 transfers the noncapsulated data packet 187 togetherwith the packet transfer message 188 to the temporary address γ ofmobile host 146, which is attached to the network C.

The visitor migration communication control device 109 notifies thestationary host 151 that the mobile host 146 is attached to the networkA instead of the network C by sending the mobile host transfer message189 where the home address α is set in the temporary address field 139.Then, the stationary host 151 transmits the noncapsulated data packet187 to the home address α, and it is transferred by the home migrationcommunication control device 101, which is employed to take the place ofthe visitor migration communication control device 109. As anotheroption, the device 109 may send the mobile host transfer message 189where the invalid address is set, such as the address where every bitis 1. Then, the home migration communication control device 101 maynotify the stationary host 151 of the home address α in accordance withthe address inquiry obtained from the stationary host 151.

The operation described the above will be employed when the visitormigration communication control device 109 ceases to provide the packettransfer service operation regardless whether or not the device 109′provides the packet transfer service.

On the other hand, the visitor migration communication device 109 mayrestart the packet transfer service even when the device 109′ ceases toprovide the service.

In this case, the home migration communication control device 101 needsto provide the visitor migration communication control device 109 withthe updated temporary address at every migration of the mobile host 146unless the mobile host migrates to the network to which another visitormigration communication control device is attached and provides thepacket transfer service. To realized it, for example, when the value ofthe autonomous flag F in the address post message is 0 to indicate thatthe device 109′ does not provide the packet transfer service, thebroadcast address Bba as the destination address of the mobile hosttransfer message, which is transmitted to the device 109, will not berenewed.

Additionally, the broadcast address as the destination address of thedata packet, which is transmitted by the mobile host 146, can bereplaced with the address Ha, Va, Va′, each of which is unique to eachdevice. The address unique to each device will be obtained by detectingthe source address of the data packet received from each device, or byemploying a so called name service.

Also in the second embodiment, the home migration communication controldevice 101 detects whether or not the mobile host 146 is attached to thesame network from what is held as the temporary address in the addresshold unit; to be precise, whether or not the home address α is held asthe temporary address. However, this can also be detected by knowing inwhich table the temporary address is held. For example, when the device101 and the mobile host 146 are attached to the same network, the firsttable holds the addresses, such as the home address α; whereas, thesecond table holds the addresses when the device 101 and the mobile host146 are attached to the different network from each other. Value of theautonomous flag F, 0 or 1, can also be utilized in the same way.

Further, the home migration communication control device 101 and thevisitor migration communication control device 109, 109′ may be employedas a host such as the mobile host 146 or the stationary host 151.

Finally, the home migration communication control device 101, thevisitor migration communication control device 109, the mobile host 146,and the stationary host 156 may be constructed identically and can bereplaced with each other.

Although in the embodiment the application unit 124 starts its operationbefore being notified of updated temporary address β; therefore italways transmits the data packet to the home address α of the mobilehost 146, it can transmit the data to the temporary address β if isstarts its operation after obtaining the temporary address β.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to be notedthat various changes and modifications will be apparent to those skilledin the art. Therefore, unless otherwise such changes and modificationsdepart from the scope of the present invention, they should beconstructed as being included therein.

What is claimed is:
 1. A mobile node migration control unit in amigration communication control device, the migration communicationcontrol device being constructed to control a communication between amobile node which migrates across networks and obtains an addressassigned on each network and a partner node which is a communicationpartner of the mobile node, being placed on the mobile node andcomprising: migration post means for transmitting to a packet transfermigration control unit a migration post message which indicates anupdated address of the mobile node when the mobile node migrates toanother network, the packet transfer migration control unit forreceiving a packet which was transmitted by the partner node to anoutdated address of the mobile node, the outdated address assigned whenthe mobile node migrated to a network to which the migration controlunit for packet transfer is attached, generating a conversion packetwhich holds the updated address instead of the outdated address, andtransmitting the conversion packet; and packet resumption means forreceiving the conversion packet from both the packet transfer migrationcontrol unit and the mobile node, and resuming an original packet fromthe conversion packet.
 2. The mobile node migration control unit ofclaim 1 further including an address post means for transmitting anaddress post message which indicates the updated address of the mobilenode.
 3. The mobile node migration control unit of claim 1 furtherincluding: address post message receiving means for receiving an addresspost message which indicates an updated address of the mobile node froma packet transfer migration control unit, the packet transfer migrationcontrol unit transmitting an address post message which indicates theupdated address of the mobile node to the partner node; and packetconversion means for converting a destination address of a packet, thepacket to be transmitted to the mobile node, into the updated addressindicated by the address post message, and transmitting it to the mobilenode.
 4. A mobile node migration control unit in a migrationcommunication control device, the migration communication control devicebeing constructed to control a communication between a mobile node whichmigrates across networks and obtains an address. assigned on eachnetwork and a partner node which is a communication partner of themobile node, being placed on the mobile node and comprising: a migrationpost unit transmitting, to a packet transfer migration control unit, amigration post message which indicates an updated address of the mobilenode when the mobile node migrates to another network, the packettransfer migration control unit for receiving a packet which wastransmitted by the partner node to an outdated address of the mobilenode, the outdated address assigned when the mobile node migrated to anetwork to which the migration control unit for packet transfer isattached, generating a conversion packet which holds the updated addressinstead of the outdated address, and transmitting the conversion packet;and packet resumption unit receiving the conversion packet from both thepacket transfer migration control unit and the mobile node, and resumingan original packet from the conversion packet.